# Error P0420, Cat efficiency below threshold?



## unclejemima (Sep 1, 2010)

Have approx 1000 km on the xtrail since I got and now I'm got a check engine soon light yesterday.

Pulled the code a friends house with a OBB2 reader (dealer wanted $170 to pull the code!!!!) and got error P0420, Catalytic converter system- efficiency below threshold

Performance has not been affected and drives fine. Xtrail has about 190k km on it.

Does anyone have experience with this error? Can I ignore it?

Thanks!


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## quadraria10 (Jul 6, 2010)

Hi UncleJemima
Read this thread contains all you need to know
http://www.nissanforums.com/x-trail/226153-06-x-trail-catalytic-converter.html

If its driving well and getting good mileage, its probably an o2 sensor issue. Yours have probably never been replaced, and are long past due. Get the NTKs for both upstream and downstream. The computer uses them in conjunction with other engine sensors. You can probably ignore it for a bit but your engine wont be operating quite right which will eventually foul your catalytic-converter. Good luck with it.


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## unclejemima (Sep 1, 2010)

quadraria10 said:


> Hi UncleJemima
> Read this thread contains all you need to know
> http://www.nissanforums.com/x-trail/226153-06-x-trail-catalytic-converter.html
> 
> If its driving well and getting good mileage, its probably an o2 sensor issue. Yours have probably never been replaced, and are long past due. Get the NTKs for both upstream and downstream. The computer uses them in conjunction with other engine sensors. You can probably ignore it for a bit but your engine wont be operating quite right which will eventually foul your catalytic-converter. Good luck with it.


Thanks for the reply. Damn this money pit car...one thing after another. I suppose thats what you get when buying used.

Do you have a PN or link for the NTK o2 sensors? Amazon or ebay?

Thanks!


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## quadraria10 (Jul 6, 2010)

I provided a link to order them in the other thread. You are welcome to copy the NTK part numbers and search Amazon for vendors. I am sure Napa will sell them as well. FYI, if you do a little research you could use the manual method for getting and clearing engine codes, and it wont cost you a cent. Otherwise you can buy a bluetooth code reader for under $20 off ebay or amazon. 
Should you have bought new? I think you got a better vehicle than the new or first gen Rogue. It is 10 years old though, someone got rid of it for a reason and and I am sure you payed less than 20% of its cost new. You cannot expect perfection. Your issues so far are all known and are relatively cheap to fix. Mind you, the dealer would have charged you more than a grand to replace your oil cooler, and if you let them, they will replace your precat manifold for around $2000. This forum contains numerous examples for how to keep maintenance and repair costs under control, take advantage of it, rather than letting the dealer possibly take you to the cleaners.
Lastly, in addition to the O2 sensors, you should look into getting the cam and crankshaft sensors replaced if they have never been changed. Same deal with your plugs and different fluids, unless you know when they were replaced last. If you have a 4wd version , changing the transfer case and rear diff gear oil every 50,000 kms or so is good protection.
In my books its best to spend more on maintenance if you want to avoid as best you can some expensive repairs down the road.


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## anjp (Jul 3, 2016)

Don't mean to hijack this thread but I'm getting a P0420 code as well. I read the thread @quadraria10 posted.

How do I know if I need to replace the catalytic converter or the oxygen sensors? I don't want to be replacing parts willy nilly.


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## quadraria10 (Jul 6, 2010)

Hi anjp
Your o2 sensors are a wear item that require replacing at periodic intervals, your precat manifold goes bad because of fouling from excessive gas consumption, and or burning excess oil or coolant. If your o2 sensors are not working properly you will be using too much gas and that will eventually cause your catalytic converter to fail. Its not a case of throwing parts at it willy nilly, rather its taking an intelligent approach to the problem. Given the age and mileage its much cheaper to start with replacing the sensors. It makes no sense to me to replace the precat manifold, and then to reuse your 10 year old sensors in it. That would then be a great way to begin spoiling the new precat and still have the car run poorly. Moreover if you want your exhaust system to last as long as possible, you want your engine to be running as efficiently as possible, and that requires good o2 sensors.


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## molly (Oct 31, 2014)

unclejemima said:


> Have approx 1000 km on the xtrail since I got and now I'm got a check engine soon light yesterday.
> 
> Pulled the code a friends house with a OBB2 reader (dealer wanted $170 to pull the code!!!!) and got error P0420, Catalytic converter system- efficiency below threshold
> 
> ...


My two cents...Find a good mechanic that is not at a dealer!!! We learned the hard, and very expensive way...Just ask around, as you want one based on others recommendations. We ended up finding two, and alternate between them. One charges $70.00/hr, and one charges $90.00/hr. And they both are very honest, not wanting to do anything unless I really need it... I have tried various things for my code P0420. Changed both 02 sensors, cam and crankshaft sensors...still comes back. I may get a new gas cap, as per a comment by chadn, another member on here! Good luck! Oh, and I am at leaning heavily on 347K.


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## unclejemima (Sep 1, 2010)

For quick reference, here is the NTK part numbers per quadraria10 from the other thread...

NTK 24298 upstream sensor ( 60.82 cdn) and the downstream NTK 24407 (50.71)


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## unclejemima (Sep 1, 2010)

molly said:


> One charges $70.00/hr, and one charges $90.00/hr


I'm assuming you don't live in Alberta ;-)

Dealer charges $165/hr and the best I can find for a normal mechanic shop that does reputable work is $120.

I'm hoping the o2 sensors will fix mine. 

Molly, do you really have 347K mileage on yours?!


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## quadraria10 (Jul 6, 2010)

For some reason I feel like eating pancakes for breakfast...
With regard to 02s sometimes they go on sale on Amazon, and you can get an even better deal. Molly is in Alberta so maybe she can help you a bit, but of course you may be in different cities.
Why are labour charges so expensive in the land of no provincial sales tax and low income taxes? Its kind of curious, surely the private market is not supposed to work that way, but I guess there must be a shortage of mechanics in the province forcing wages through the roof.
Here in Gatineau dealer charges 95 + 15% sales tax (GST + PST) per hour and most shops are between 80 and 90 per hour now. 

Changing the oxygen sensors can be a bit of a pain but its very doable as a diy job. I wrote a thread about it here after doing mine.

Of course changing one's gas cap might be the easiest diy ever--- hint hint Molly.


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## molly (Oct 31, 2014)

Sorry for the late reply! I don't always get emailed notices, for some reason... As Quad says, I do live in Alberta, over an hour SW of Calgary. My mechanics live in Nanton, and west of Nanton. They are great guys! Dealer rates seem to vary from $120-140.00. Ouch!!! And yes, I do have that many kms. on mine...Quad told me I should wear that mileage like a badge!! 

And yes, Quad, I plan to order a gas cap...on my list of things to do! Along with one of those headlight renewal kits!


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## rogoman (Dec 16, 2004)

anjp said:


> Don't mean to hijack this thread but I'm getting a P0420 code as well. I read the thread @quadraria10 posted.
> 
> How do I know if I need to replace the catalytic converter or the oxygen sensors? I don't want to be replacing parts willy nilly.


QUAD's suggestion is good about replacing both upstream and downstream O2 sensors due to the large amount of miles on the vehicle. However here are some other possible causes for the P0420 code:
● Intake system vacuum leaks
● Bad fuel injector
● Fuel injector leaks
● Spark plugs dirty


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## anjp (Jul 3, 2016)

rogoman said:


> QUAD's suggestion is good about replacing both upstream and downstream O2 sensors due to the large amount of miles on the vehicle. However here are some other possible causes for the P0420 code:
> ● Intake system vacuum leaks
> ● Bad fuel injector
> ● Fuel injector leaks
> ● Spark plugs dirty


Thanks. It's an intermittent code and doesn't always show up so I'm wondering how to go about diagnosing. I can drive a full tank of fuel and get nothing, and then sometimes get it every couple days. 
I'll start with spark plugs and 02 sensors I suppose.

cheers


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## rogoman (Dec 16, 2004)

anjp said:


> I'll start with spark plugs and 02 sensors I suppose.cheers


CATs are expensive to replace so start with the easiest/cheapest first. If the spark plugs are old, replace them first and see what happens. If replacing O2 sensors, get the OEM NTK sensors as suggested by QUAD, not some other aftermarket type. 

It's possible that the fuel injectors just have dirt in them. Run some good injection cleaner, like Techron or Redline SL-1, through the system; Give the cleaner about a week or two to do it's job. 

You can check for vacuum leaks in the intake system with a vacuum gauge. Attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.


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## anjp (Jul 3, 2016)

I started with the spark plugs yesterday. I'm not sure if they were original (they were the NGK OEMs) but they were a little corroded and time to replace anyway. 
There's 279,000 kms on this one so it's hard to believe they are original. Who knows. 

Now I'll wait a bit and see what happens.


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## unclejemima (Sep 1, 2010)

anjp said:


> I started with the spark plugs yesterday. I'm not sure if they were original (they were the NGK OEMs) but they were a little corroded and time to replace anyway.
> There's 279,000 kms on this one so it's hard to believe they are original. Who knows.
> 
> Now I'll wait a bit and see what happens.


Did you reset the codes after the swap? I don't know if it will go away on its own?


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## anjp (Jul 3, 2016)

unclejemima said:


> Did you reset the codes after the swap? I don't know if it will go away on its own?


Yes I cleared the code. Been doing that off and on for a couple months anyway


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## quadraria10 (Jul 6, 2010)

I have no clue as to if they were original either, but I am willing to bet your 02s are original and that they are operating at the margins. At 279,000 you should be ready to replace your third set by now. By way of example at 175,000, I am on my third set of plugs. First changed at 105,000, and then again at 160,000. o2s changed at 150,000 kms. I am still completely original for exhaust system and no cat related problems whatsoever. Its not a fluke.


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## anjp (Jul 3, 2016)

quadraria10 said:


> I have no clue as to if they were original either, but I am willing to bet your 02s are original and that they are operating at the margins. At 279,000 you should be ready to replace your third set by now. By way of example at 175,000, I am on my third set of plugs. First changed at 105,000, and then again at 160,000. o2s changed at 150,000 kms. I am still completely original for exhaust system and no cat related problems whatsoever. Its not a fluke.


Recommendations on O2 sensors brand?

1. NGK OEMs, both up/downstream for $183 + tax at Cdn Tire

2. BOSCH 15518 & 15525 up/down for $111 + tax RockAuto 

3. NTK 24407 & 24298 up/down for $114 + tax RockAuto

Heard good things about the BOSCH's and NTKs. 

cheers,
ap


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## otomodo (May 23, 2008)

I bought booth from rockauto 114$ tx and shipping inc.
It took 4 days to get here

HO MALA?
Acarta pà grota


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## quadraria10 (Jul 6, 2010)

I got mine off Amazon.com a few years back when the Cdn dollar was at par. Got both for around $80.
Anjp the NTK's are the originals. Its the same company that makes NGK but those are sparkplugs whereas the NTKs are O2 sensors.
Canadian Tire calls them NGK but if you look at the illustrated box they are NTK. Save some bucks and get them from RockAuto like Otomodo suggests.

You can get both for 81.87 US on Amazon.com not .ca at the moment but that is more expensive than RockAuto at todays exchange rate, and they no longer ship to Canada-- so RockAuto is the best deal.
Oops spoke too fast Wrench Monkey has them on sale and both will cost 111.40 + tx with free shipping in Canada.

https://www.thewrenchmonkey.ca/auto-parts/nissan/x-trail/2006/oxygen-sensor/


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## MikeHJ (Mar 7, 2017)

unclejemima said:


> Pulled the code a friends house with a OBB2 reader (dealer wanted $170 to pull the code!!!!) and got error P0420, Catalytic converter system- efficiency below threshold
> 
> Performance has not been affected and drives fine. Xtrail has about 190k km on it.
> 
> ...


Just finished dealing with this on my other car, not my Xtrail.

P0420 means the cat is not operating within the efficient temperature range, either too cold or too hot.

It takes a while for the exhaust and cat to heat up to optimal operating range, so if you've reset the code and then just done some quick drives around the neighborhood it might not show up again for a while.

If it is running too cool, then you might have an exhaust leak between the manifold and the cat or in the cat. If too hot, then it could be clogged due to a host of reasons. Or it could be bad sensors as others have mentioned

If you want a simple way to start, look to see if you have good pressure coming out of the tail pipe. In my case, there was exhaust coming out, but it wouldn't blow out a match unless I had it up close (not that I used a match, just an example.)

Borrow or buy a laser thermometer (they"re not too expensive) and check to see if there is a big temp variation between the pipes front and back of the cat. If there is then you could be clogged.

Borrow or buy a cheap code reader that shows live data. I got one at Walmart for $35. Plug it and start the car. Check if you just have the one p0420 code or if there are additional codes. If there are other codes, then check them out first. They could be causing the 420 code. One o2 sensor should be switching voltages and the other should be fairly steady. If one "spikes" and sticks at an abnormal voltage, then goes back to normal operation, then you've probably got an o2 sensor that is starting to die.

A decent code reader that displays live and freeze frame data is a good cheap investment for any car owner.

In my case, my air intake manifold gasket was leaking and things were running lean (and undetected). The extra heat melted some of the honeycomb inside the cat and it partially clogged. I was hoping it was just a leak or a bad O2 sensor, but I'm not that lucky.

Sadly, my experience has been that, on older cars with an unknown running history, P0420 usually comes down to the cat. Due to the cost, it is worth checking out every other possibility first, but you can run up a tidy bill swapping o2 sensors and fuel injectors only to end up changing the cat anyway. The car has probably been running rich or lean for a long time and the cat is fouled or clogged.

The good news is that unless it clogs completely, the car will still run. Your gas mileage will suffer, you'll be polluting and won't pass emissions testing, but you're unlikely to get stranded.

Look on youtube for "Eric the Car Guy" channel. He has a good video walking thru diagnosing the P0420.or read
easterncatalytic.com/education/tech-tips/the-misleading-nature-of-the-po42o-code/


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## otomodo (May 23, 2008)

When i ve changed both o2 sensors the next day i had that code and it was simply the connector not well connected.
His code could be a stripped wire or broken wire.
Even a bad connection or verdigris.

HO MALA?
Acarta pà grota


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## anjp (Jul 3, 2016)

Thanks, I do have a laser thermometer so I will check pipe temperatures. I don't think there are any (obvious) leaks and the tail pipe has a good gust coming out of it. Maybe there's a small leak around a gasket connecting some old pipe but it's hard to know what gets detected.
Should there be any difference in pipe temperature before/after o2 sensors, catalytic converter, and muffler?

cheers,



MikeHJ said:


> Just finished dealing with this on my other car, not my Xtrail.
> 
> P0420 means the cat is not operating within the efficient temperature range, either too cold or too hot.
> 
> ...


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## MikeHJ (Mar 7, 2017)

anjp said:


> Thanks, I do have a laser thermometer so I will check pipe temperatures. I don't think there are any (obvious) leaks and the tail pipe has a good gust coming out of it. Maybe there's a small leak around a gasket connecting some old pipe but it's hard to know what gets detected.
> Should there be any difference in pipe temperature before/after o2 sensors, catalytic converter, and muffler?
> 
> cheers,


A Cat converter is basically an oven that heats up as your exhaust gases heat up. Once it gets hot enough, it basically "bakes" your exhaust gases in the presence of various rare earth elements (plated on the surface of the honeycomb inside). The rare earth elements are the catalyst: they "facilitate" the chemical reaction, but in the end, remain unchanged. The chemical reaction they facilitate is to break down unstable Nitrogen/Oxygen molecules (NOx) to more stable molecules. If cars didn't have cat converters, the NOx would break down in the atmosphere and form various gases (like ozone) which contribute to smog.

Your code indicates that the cat converter is just never getting hot enough to reach the temperature range where the catalytic reaction occurs.

This can happen for 3 main reasons: 1) you have a leak somewhere in the exhaust before it reaches the cat, allowing hot exhaust to escape or cool outside air to enter. 2) the cat is clogged and the exhaust gases are just not circulating thru very well, preventing hot gases from getting in there quickly before they cool off or 3) the O2 sensors are just not reading things correctly because they're old and fried. Basically a false code.

Drive your car until it is good and hot, not just until the coolant temp gauge says it's hot. Take it out for a good freeway run for 45 minutes. Let it idle while you check the temps with a laser thermometer. Measure the pipes just before and after the cat. Have a buddy rev the engine and measure at various RPM's. There should not be a huge difference in temperature before and after the cat. If there is a big difference, then your cat may be partially clogged. If it is partially clogged, then you might see a big temp difference at idle, but less of a difference as the engine revs higher. The increased pressure at higher revs might force more gases thru.

If that looks good, then I'd check the O2 sensor voltage changes with a live data scan tool next, simply because you don't have to take anything apart. You can just watch the voltages flip around while the engine is running. If anything is out of whack, check the O2 sensor in question and replace if necessary.

3rd, I"d start looking for leaks pre-cat. Which is more of a pain, so I like to do the other checks first. 

Cat's aren't cheap, but neither are o2 sensors and exhaust pipes. Better to spend some time diagnosing before you start swapping parts (unless you have a Upull place nearby where you can pick up things dirt cheap)


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## quadraria10 (Jul 6, 2010)

Great post MikeHJ, informative and practical!


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## MikeHJ (Mar 7, 2017)

quadraria10 said:


> Great post MikeHJ, informative and practical!


Thanks, but it more really just a list of cheap/semi-useful things you can do before you start attempting to undo rusty exhaust bolts and stuck O2 sensors. And then pay to replace the ones you broke when they weren't even the problem in the first place.

The thing about cat converters is that they don't really "wear out". They should work for the life of the vehicle unless something happens to them. Rust or road damage is pretty obvious, so if you put a new one on, you can pretty much rest easy that it will last until the road salt damage or pothole chunks get to it again.

The concern is that your engine is doing something like running too lean and melting the honeycomb or running too rich and fouling the honeycomb with hydrocarbons. If that is what made your first cat go bad, then it will do the same thing to your replacement cat soon enough.You may still have to replace the cat when you get the P0420 code because it's too late to save it. But you don't want to just swap in a new cat, clear the codes and walk away thinking you "fixed" the issue. If cats were only $50, that's probably what I'd do, but they're not $50 so I don't want to swap them out every year.

The first time I had the P0420 code, I grasped at every "cheap" possible solution to avoid spending $800 on a cat. I swapped o2 sensors, changed manifold gaskets, broke manifold studs, fixed manifold studs, changed flex pipes, etc. Probably spent more time and money avoiding touching the cat than the cat was worth. And then bit the bullet, took off the cat and a big chunk of the honeycomb fell out in my hand. D'oh!

You don't have to spend $80 on a new O2 sensor and hope that it was causing the problem or new plugs or gaskets, etc. They certainly could be the problem, but swapping parts is an expensive way to diagnose things.


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## quadraria10 (Jul 6, 2010)

All true, but as I have posted before O2 sensors are wear items whose proper function helps the ecu ensure proper fuel trim. And moreover if you have a bad cat it will have affected the sensors as well. Its a false economy in my book for someone with a 10+ year old X trail to reuse their old sensors if they replace the front cat manifold on our engines. All I can add is that fortunately a new one doesn't cost 800.
Anyway my x trail is now 10 and half years old 183,000 kms of mainly city driving and everything about the exhaust is still original. I did have a flange cut out and overpiped, and a couple of brackets rewelded during its life so far, but happy to report no obvious issues on the horizon.
In the interest of maintaining engine health I plan to replace the pcv valve, and the ignition coil boots in the near future. The X has been great, hoping it can remain so for a few more years yet. Hope yours lasts as well.


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## MikeHJ (Mar 7, 2017)

quadraria10 said:


> All true, but as I have posted before O2 sensors are wear items whose proper function helps the ecu ensure proper fuel trim. And moreover if you have a bad cat it will have affected the sensors as well. Its a false economy in my book for someone with a 10+ year old X trail to reuse their old sensors if they replace the front cat manifold on our engines. All I can add is that fortunately a new one doesn't cost 800.


Well, we'll have to agree to disagree about O2 sensors. I just monitor them with a scan tool and change them when their operation goes funky. If they change voltages as they should, they don't need to be changed. If a bad cat fouled them or fried them, then they won't change voltages as they should. 

And yeah, the Xtrail cat doesn't cost that, but my last car's did.

I have a slightly different view of my Xtrail. It's the same age as yours and has about the same mileage (185km) But I only bought it a year ago and I only paid $3000 for it. I'll fix it and maintain it, but I won't spend a large % of its total value on repairs. I'll get rid of it. As much as I like it so far, it is still a disposable item to me. I don't carry collision or comprehensive insurance on it, for example, just liability.


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## quadraria10 (Jul 6, 2010)

I hear you about spending on it. However in our case, we bought it when it was 3 years old with less than 58,000 kms and payed close to 20,000 with txs and financing. List price for ours when new was 31K. Its been great, and I find it still compares quite favorably with any of the new cuvs on the market. I thought of replacing it with a 2012 Forester but decided they are pretty darn similar, and I enjoy having a payed off reliable vehicle. My attitude has been to be proactive when it comes to replacing things I can foresee going bad in the not too distant future, and keeping on top of fluid changes at appropriate intervals. So far the X trail has been the most reliable trouble free car I have had, which includes a few cars we bought new. Guess I finally learned not to cheap out on maintenance, mainly by making it a hobby and doing a lot of it myself. Sounds like you have a lot more experience in this regard, not to mention a couple of tools I do not own lol. All I can say is you bought well my friend and would have payed more for a similarly used crv rav, forester which were not better vehicles than the less well known x in canada. In BC you would have had to pay a minimum of double what you payed to find one. At 3,000 you got a heck of a deal. If you maintain it, I don't think its going to depreciate a whole lot any time soon. Heck you could probably sell it this spring or summer for more than you payed.


s


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## anjp (Jul 3, 2016)

MikeHJ said:


> Well, we'll have to agree to disagree about O2 sensors. I just monitor them with a scan tool and change them when their operation goes funky. If they change voltages as they should, they don't need to be changed. If a bad cat fouled them or fried them, then they won't change voltages as they should.
> 
> And yeah, the Xtrail cat doesn't cost that, but my last car's did.
> 
> I have a slightly different view of my Xtrail. It's the same age as yours and has about the same mileage (185km) But I only bought it a year ago and I only paid $3000 for it. I'll fix it and maintain it, but I won't spend a large % of its total value on repairs. I'll get rid of it. As much as I like it so far, it is still a disposable item to me. I don't carry collision or comprehensive insurance on it, for example, just liability.


What's the criteria for funky operation?  

Mine still switch voltages during operation....But how do we know they're switching to the correct voltages?

Sent from my LG-D852 using Tapatalk


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## quadraria10 (Jul 6, 2010)

From NGK web site

NGK Spark Plugs Canada » Tech Info » Oxygen Sensors

''Oxygen sensors are subjected to a considerable amount of wear & tear, ageing, and extreme temperatures even under normal operating conditions. Harmful contaminants, however, that may be present in your vehicle's exhaust stream can significantly reduce the life span of an oxygen sensor. Factors that contribute to the life span of the oxygen sensor include the location of the sensor on the vehicle's exhaust system. Sensors located directly in the manifold (usually 1 & 2 wire sensors) typically have a shorter life span due to the higher temperatures under which they operate and the increased exposure to harmful exhaust particulates (unspent fuel/oil). Conversely, sensors that have a heater in the thimble element (3 & 4 wire sensors) are more quickly brought up to operating temperatures, and therefore, are thus exposed to less harmful contaminants and operate under lower exhaust temperatures as they can be located further downstream in the exhaust system.

As the world's largest manufacturer and supplier of oxygen sensors, NTK brings to the aftermarket comprehensive knowledge of current and future OEM R & D, technology, and experience. All NTK oxygen sensors are extensively tested during manufacturing to guarantee quality, reliability, and above all, always meet or exceed the original equipment specifications. NTK oxygen sensors are designed for longer service life (from 80,000 up to 150,000km) and have been recognized as a leader in the industry. It is, however, always a good idea to have oxygen sensors checked at each tune-up and/or regular service intervals. With the harsh actual conditions in your vehicle's exhaust coupled with the higher temperatures of today's hotter running engines, NTK generally recommends checking your oxygen sensor at every 60,000km and/or every tune-up for any excess ageing or premature signs of sensor poisoning and contamination. Replace faulty sensors with confidence in a product and name you can trust, NTK Oxygen Sensors.''

I do mainly city driving--lots of short trips under a half hour. I replaced mine at 150,000 assuming they had seen better days. It did improve engine idle and gas mileage slightly.


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## MikeHJ (Mar 7, 2017)

anjp said:


> What's the criteria for funky operation?
> 
> Mine still switch voltages during operation....But how do we know they're switching to the correct voltages?
> 
> Sent from my LG-D852 using Tapatalk


You're looking for consistent, timely operation centered around the midpoint of the voltage range.

Sticking at a voltage for several seconds, consistently and frequently switching to the upper or lower extremes of the range, upstream sensor failing to mimic the downstream, downstream sensor switching at the same or a faster rate than the upstream are warning signs.

If your OBD2 device or software has a graphing function, then you want to see a relatively smooth consistent waves over time.

If they're going bad, they get less sensitive and more sluggish and the graphed lines get more inconsistent and more out of sync with each other. That will happen normally, but in a good running engine, it takes a long time (typically 140-160km in an ODB2 compliant engine) If it happens more frequently than that, then you probably have something else going on. We both have around the same mileage (185km) so we both should probably have had to change them once by now.

If you're trying to diagnose the P0420 code that doesn't also have an o2 sensor code, and your existing o2 sensors seem to switch quickly enough, then you can change them if you like, but move on with your diagnostic.


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## MikeHJ (Mar 7, 2017)

quadraria10 said:


> I hear you about spending on it. My attitude has been to be proactive when it comes to replacing things I can foresee going bad in the not too distant future, and keeping on top of fluid changes at appropriate intervals. So far the X trail has been the most reliable trouble free car I have had, which includes a few cars we bought new.
> 
> . At 3,000 you got a heck of a deal. If you maintain it, I don't think its going to depreciate a whole lot any time soon. Heck you could probably sell it this spring or summer for more than you payed.
> 
> ...


So far, I'm pretty pleased, but the X trail has a ways to go before it becomes the most reliable car I've ever owned. That award goes to a 99 Suzuki Grand Vitara. I replaced exactly 1 wheel bearing in that thing in 13 years before the rust finally got into the frame. And it still started on the first key turn and ran well after spending the entire winter buried in a snow drift.

My Exxy runs well, but in the one year I've owned it I've had the interior temp sensor fail, the blower fan bushing squeak, pulled a door handle off in addition to doing a partial brake job, replaced the mid pipe on the exhaust, had the alternator go and had to pay for a new evap pipe when I got the fuel filler neck recall done. I knew about the brakes when I bought it and the other things were relatively minor, but still. 

For the price I paid, I'm very pleased, but if I had paid closer to true market value I'm not convinced I'd be as enthusiastic.


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## quadraria10 (Jul 6, 2010)

If in 13 years of ownership you only replaced one bearing, I would not have rushed to buy it used. Guess you got an exceptional one, didn't drive it, or pretty much neglected it. Of course, if your X trail is an 05 sold in 04 it could be pushing 13 years of age now as are some being sold used currently. For 3K you have to expect to put some money into it. In my experience people get rid of/sell cars because they know something or a few things will require some money to repair. Anyway, the thing I like about this forum and our section particularly is that a good number of us, help each other out and post good info on how to maintain them and deal with problems. I, and others I am sure, appreciate your comments along those lines. Have a great Easter.


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## anjp (Jul 3, 2016)

Looking at the graphing function of my obd2, the sensor is switching back and forth between the extremes pretty quickly.... at least, if I"m reading it correctly.

So I'm swapping out the o2 sensors. I"m using:
NTK 24298 (Upstream) and NTK 24407 (Downstream). If the NTKs are the OEM parts then these sensors have definitely been changed. Or the upstream one has anyway...

Below are upstream and downstream sensors (new = left, old = right)... Yes, I'll take the thread covers off before installing.


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## anjp (Jul 3, 2016)

Well the code came back...
It went about a week of driving after the sensor switch clean as a whistle...but it's back now and stays after multiple deletes. 

I guess I can rule out the O2 sensors and move on to the cat. 

Cheers,
Andrew 

Sent from my LG-D852 using Tapatalk


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## X-hale (Apr 17, 2017)

I had the same experience. I replaced both O2 sensors and the code came back. In all the years of car ownership and many, many code PO 420 experiences, this is the first time that I think a cat replacement may be final solution. There's no smog testing here though so I'm in no big rush.


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## chadn (Jan 28, 2010)

X-hale said:


> I had the same experience. I replaced both O2 sensors and the code came back. In all the years of car ownership and many, many code PO 420 experiences, this is the first time that I think a cat replacement may be final solution. There's no smog testing here though so I'm in no big rush.


If you're interested, I have a brand new in box catalytic converter for the x-trail I would be willing to sell. I got it to replace mine when my x-trail started throwing the P0420 code. My code went away with new o2 sensors.

I also have a set of o2 sensors that I probably won't need. Brand new as well.


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## X-hale (Apr 17, 2017)

chadn said:


> If you're interested, I have a brand new in box catalytic converter for the x-trail I would be willing to sell. I got it to replace mine when my x-trail started throwing the P0420 code. My code went away with new o2 sensors.
> 
> I also have a set of o2 sensors that I probably won't need. Brand new as well.


I may be interested. Send me a PM with your price, shipping and location. Thank you


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## tonyvancity (Jan 2, 2017)

there is a Toronto muffler/ Cat supplier advertising everywhere including this kijiji Ad.....Nissan X-Trail 2.5L Exhaust Catalytic Converter 2005-2006 | other parts, accessories | City of Toronto | Kijiji ....states FREE SHIPPING on orders over $150 ...but no actual price...i imagine they want to be emailed for the price. 
https://www.ultraexhaust.ca/


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## tonyvancity (Jan 2, 2017)

https://www.ultraexhaust.ca/collect...-catalytic-converter?variant=35064601168...on sale at $330.....too rich for me at the moment.


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## X-hale (Apr 17, 2017)

tonyvancity said:


> https://www.ultraexhaust.ca/collect...-catalytic-converter?variant=35064601168...on sale at $330.....too rich for me at the moment.


The Ebay price from them is much, much cheaper than $330 even with the exchange. I've checked just about everywhere.


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## quadraria10 (Jul 6, 2010)

Here is an ebay site from Canada selling one for less than 160 with delivery included

Fits Nissan Altima 2.5L Manifold Catalytic Converter 2002 TO 2006 DirectFit

That said, if I remember Chadn's was from the US, nicer quality and comes with heat shield.

Quality of materials and welding seems to vary on these. For example here is a bit higher priced one that gives you more than the previous listing but will run about 215 Cdn all in.

http://www.ebay.ca/itm/BRAND-NEW-EX...ash=item33b09cd433:g:KzAAAOSwqYBWpuYI&vxp=mtr

or

http://www.ebay.ca/itm/For-Nissan-A...ash=item3d14c24a3c:g:fBwAAOSwEeFVAEvg&vxp=mtr

And of course a good thing is both of these the listers have 99.5% satisfaction ratings and have sold a bunch of them


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## anjp (Jul 3, 2016)

Has anyone changed the cat on their 2.5L? I'm looking for a time estimate.
It seems like it's pretty tight in there and would need to take a few other things out to create a workspace.


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## MikeHJ (Mar 7, 2017)

X-hale said:


> The Ebay price from them is much, much cheaper than $330 even with the exchange. I've checked just about everywhere.


I've purchased a couple of cat converters for other cars from Ultra Exhaust. I had heard that they do work but they won't last as long as an OEM.

I took a long look at them at them when they arrived and the only difference that I noticed was that the honeycomb inside was not as fine as the OEM. Basically, not as much surface area. That said, everything else appeared good: good welds, same gauge pipe, etc.

Since I was installing them myself (no labour cost)on high mileage cars, I was willing to take the chance. They worked as expected: codes cleared and didn't come back, the car passed emissions tests, etc. I didn't own all the cars long enough to see them fail, but I did own some of the cars for another 3 years and drove another 75k km. For the price difference, I felt that they were a pretty solid purchase for my needs. If I had to replace them every 4-5 years, then that was okay. If I was putting them in a younger car, paying for labour and needing to get 10 years out of them before replacement, then I might have a different opinion.


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## X-hale (Apr 17, 2017)

Thanks for your comments MikeHJ, very helpful and informative.


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## RangerRay (Oct 10, 2013)

I just got P0420 recently on my Xsey. My mechanic told me that the catalytic converter is obsolete and needs to be replaced, but that they need to replace the whole exhaust manifold to do it. According to him, it is all one part, or it is extremely difficult to replace the cat. On top of this, he said he checked all his suppliers in the city and even a supplier in Vancouver that specializes with aftermarket import parts and couldn't find a new aftermarket exhaust manifold for the X-Trail. I have noticed a drop in fuel mileage and I commute an hour each way on highways everyday and would like to get it fixed. Are there any recommendations? According to some of the earlier posts, I may not have to replace the entire manifold, which according to him is obsolete and a new one can't be found.

My Xsey has over 229,000 km on it , if that makes a difference.


Thanks!


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## quadraria10 (Jul 6, 2010)

Have you read this thread Ranger Ray? Ours have the same qr25de engine as found in 02-06 Altimas and a cat manifold for one of those will do just fine. If you never changed your O2 sensors... anyway its easy for you to research this a bit

https://www.obd-codes.com/p0420

Here is an example of an Altima one that would work

http://www.rockauto.com/en/moreinfo.php?pk=3862263&cc=1432235&jsn=434

You could also do a search on Kijiji or Ebay and you will find aftermarket exhaust that make them at a decent price.
Again though in your shoes I would try installing new o2 sensors before full replacement, as you will need new ones in any case.


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## X-hale (Apr 17, 2017)

Your mechanic is telling the truth. The cat and manifold is one piece. I don't know if these guys will ship: https://www.kijiji.ca/v-other-auto-parts-and-accessories/city-of-toronto/nissan-x-trail-2-5l-exhaust-catalytic-converter-2005-2006/1063779012

Mine has 215,000 km and I just replaced the cat after first trying the O2 sensors.


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## tonyvancity (Jan 2, 2017)

https://www.ultraexhaust.ca/ check out this website based out of Toronto....free shipping over $150. I texted/emailed them a few times regarding an aftermarket muffler for my 06 Xtrail and they replied very quickly. https://www.ultraexhaust.ca/


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## tonyvancity (Jan 2, 2017)

https://www.ultraexhaust.ca/collect...500cc-i4-gas-dohc-se-sport-utility-4-door-awd NON CARB Compliant ----ULTRA EXHAUST 43136 DIRECT-FIT CATALYTIC CONVERTER (NON C.A.R.B COMPLIANT)
$330.00 CAD ( regular $462.00 CAD) and ULTRA EXHAUST 284-259 EXHAUST PIPE
$101.00 CAD


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## quadraria10 (Jul 6, 2010)

Just to point out the Rock Auto link I provide is 213 cdn and can be shipped for as little as $21. Also includes the gasket, and other hardware needed. Also available on Amazon
Amazon.com: Eastern 40810 Direct Fit Catalytic Converter: Automotive

though I think the price is in American dollars so it would be more expensive than RA but if you have Amazon Prime and can get free shipping it might be worthwhile.

Last thing, the old one should still have a bit of value and you may be able to get a few bucks for it from a recycler. Or your mechanic will keep it and sell it


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## cartman_to (Nov 29, 2017)

I bought a new cat converter from ultra exhaust back July 2016. It turned off my SES light and has been fine since. Paid $220ish CAD shipping included. Noticed that they raised the price since. Hth


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## RangerRay (Oct 10, 2013)

Thanks for the info guys. Much appreciated!


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## tonyvancity (Jan 2, 2017)

hi Cartman....i realize the Cat is different from replacing a muffler, but what do you notice with a brand new Cat on your Xtrail? is there any improvements in performance, throttle response, fuel economy, etc....or is it basically what a new from the factory Xtrail would be like? I ask because i personally have never had to replace any Cat on any of the vehicles i owned in my 32 years of driving history. I had a few sport mufflers swapped in (Magnaflow muffler on my 04 honda civic Si was an awesome improvement, altho not cheap...). I imagine the Cat is basically a clean air device on all vehicles and nothing to do at all with performance upgrades eh?


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## MikeHJ (Mar 7, 2017)

tonyvancity said:


> I imagine the Cat is basically a clean air device on all vehicles and nothing to do at all with performance upgrades eh?


A cat converter is a clean air device, not an upgrade. They can clog or fry out depending on how they fail, neither is good.

By law, most vehicles have to have one and they have either a neutral or a negative effect upon performance. 

They are basically an oven, heated by exhaust gases. Inside they have a fine mesh coated with rare earth metals. Once they reach operating temperatures, the exhaust gas "bakes" and a catalytic reaction occurs breaking down unstable nitrogen/oxygen compounds into more stable forms. I think the stable form is NO2, but burning hydrocarbons produces NO, NO2, NO3, NO4 (sorry don't know how to do subscript) and these forms are collectively known as NOx (where x is a wildcard number)

If allowed to exhaust directly to the atmosphere, these unstable forms will quickly breakdown to NO2 and ozone. Ozone and NOx gases are the primary form of smog. Basically, the cat converter "scrubs" the exhaust gas and makes it more stable.

The P0420 code is an warning that the cat converter is not operating in the required temperature range for the catalytic reaction to occur (either too cool or too hot) and therefore that your car is polluting, often invisibly.

The side effect of a bad cat converter is that the O2 sensors try to compensate by enriching or leaning out your air/fuel mixture. but because the cat is bad, they will consistently be on one side or the other. If too rich, then you get poor mileage, fouled injectors, fouled plugs and a build up of fuel residue. If too lean, your engine will run hotter than it should, causing all sorts of other issues over time.

Like any other exhaust part, they are subject to dents and rust, but they do last a long time. Generally they are installed at an angle so the don't get water pooling in them like other exhaust pipes and they're usually made of heavier gauge steel than the rest of the exhaust to hold the heat better.

When they degrade, it is usually the mesh inside falling apart. Sometimes it clogs the exhaust flow, sometimes it doesn't. Either way, it need replacing.


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## tonyvancity (Jan 2, 2017)

hanks MikeHJ, very informative ! Sometimes i see Ads for ''performance Catalytic converters and they are expensive and wonder if they are meant for high performance applications or just means '' will perform better service then a stock cat''. I think i need to take my Xtrail to a muffler shop one day soon as i have an annoying under carriage metallic sound...most like my heat shield. Saw it once when it was up on a mechanic's hoist and it was kinda rusty and in sad shape. Maybe the muffler shop can cheaply fabricate a new one.


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## X-hale (Apr 17, 2017)

Like you tonyvancity, I had never replaced a catalytic converter in my life. There was always some other underlying cause for the PO420. It is *the* most common OBD2 code.
On the X-Trail I tried the usual culprits and then replaced the cat. All is well since the replacement. There was a very noticeable improvement in performance and mileage.


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## MikeHJ (Mar 7, 2017)

tonyvancity said:


> Sometimes i see Ads for ''performance Catalytic converters and they are expensive and wonder if they are meant for high performance applications or just means '' will perform better service then a stock cat''.


Well, there are such things as "performance" cat converters. Generally, they are slightly larger diameter pipe or a bigger "bulge" where the mesh is inside or coarser mesh. They work by "enhancing" the exhaust gas flow and reducing back pressure. Of course, it comes at the expense of emissions quality, reducing the cleaning effect to the lowest legal level and they are pricey.

Realistically, you need to have tweaked every other engine component for maximum performance before you see any significant improvement from installing one. If you have put in high performance spark plugs, fuel injectors, O2 sensors, etc. and flashed the ECU and you're still looking for a couple of horsepower, then go crazy. Do the other enhancements first, though: they're cheaper and have more of a direct effect on performance.

Let's face it, the Xtrail is a 4 cylinder quasi SUV. Very useful to be sure, but it's usefulness lies in the body shape, ground clearance and driveability, not in horsepower, torque, towing ability or acceleration.


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## tonyvancity (Jan 2, 2017)

mikeHJ said : ''Let's face it, the Xtrail is a 4 cylinder quasi SUV. Very useful to be sure, but it's usefulness lies in the body shape, ground clearance and driveability, not in horsepower, torque, towing ability or acceleration.''------you bet, i agree. Great suv and does exactly what is designed for...moving people, cargo and occasionally getting us thru wintery road conditions. Even so , with every vehicle i owned since age 19, i like to add my own custom touches . Only thing i would like it a bit more of a sportier sounding muffler. I know it will not increase horsepower but i just want a bit more gruffer sound when i step on the gas pedal. So later this coming spring, if i can get away with under a $200 muffler upgrade i will..if not, i'm fine to drive it stock. Coming from a previously weak 127 Hp 2004 honda civic Si, i'm very pleased to have a fuel efficient and powerful enough 165 Hp small awd suv.


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## MikeHJ (Mar 7, 2017)

tonyvancity said:


> Coming from a previously weak 127 Hp 2004 honda civic Si, i'm very pleased to have a fuel efficient and powerful enough 165 Hp small awd suv.


Around town, I find the 2.5 4 cylinder adequate. Sluggish to accelerate, but adequate most of the time. It is usually empty with just me in it so I think I'd be more negative if I had 3-4 people in it regularly.

Off the asphalt (country roads and forestry roads, not bushwacking) I find the uni-body soft and the low-end torque less than okay. It still gets me where I want to go, but it is obvious that it is not meant to be doing this. It is too soft to handle bumps with any kind of speed, makes going uphill on rough roads a bouncy experience with a few ground taps. The entry and exit angles (particularly the exit with a load) look good, but just aren't enough with such a soft suspension

The interior is very good. Not stylish or super high quality, but roomy and well thought out. I've done a few 15-17 hour trips and found it comfortable and an easy highway driver.

Overall, I like it, but it is definitely a compromise between a car and an SUV


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## otomodo (May 23, 2008)

MikeHJ said:


> Around town, I find the 2.5 4 cylinder adequate. Sluggish to accelerate, but adequate most of the time. It is usually empty with just me in it so I think I'd be more negative if I had 3-4 people in it regularly.


I dare you to go for a test drive on a lexus ct 200h and drive it on eco mode. 
Have you hauled a trailer full of crushed stone with the Xtrail ? Same feeling. 

Usually i get under 6L/100km on highway, cruise control on normal mode and eco mode. Yesterday it was windier and i got 7,2L/100km average. 
I find the Xtrail too soft for a suv but once spring is here i forget about all of it s negative points.


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## tonyvancity (Jan 2, 2017)

i find , for my usages, the Xtrail to be more then adequate. I cannot compare here online my Xtrail to others, but my vehicle scoots down the streets and highways very nicely. I dont expect it to be a hardcore serious off roader like a jeep wrangler nor did i buy it for that intention. For me, i use it to take family members shopping, to get to work, to move big heavy items such as my work tool boxes, to toss my mtn bike in the cargo area, to put my dog in the back for a park adventure. It's been thru heavy rainstorms, 10 inches of crunchy-icy snow in winter and 35c hot summer days to the beach and out of town. I think some people on here misunderstand when i ask ''what can i do to improve the horsepower/performance a little?''...i'd be asking that on any vehicle i own. But i have concluded i dont have the money or desire to blow a ton of money on maybe an extra 10 horses or so. I am content the way the 2.5L engine propels the little suv just as is. Very content i have this 06 Xtrail and sometimes i wish i bought it brand new or near new when i had the chance. But oh well....the one i have now is a keeper .


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## MikeHJ (Mar 7, 2017)

It's not that I dislike it, it's that I find it too much of a compromise at times.

There are certain boat launches where it really struggles to pull a light boat trailer out of the water. And few cottage roads that I have driven for years where it ground taps. A lot of my friends have competing vehicles (Rav4, CRV, etc.) and we've been doing the exact same things for years. I've owned other SUV's as well.


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## tonyvancity (Jan 2, 2017)

MikeHJ, i understand completely....no need too explain....some things it does well for you, some not. Our Xtrail is maybe more of a car/station wagon based suv for lite duties such as the honda crv, toyota rav4, mid 1990's subaru forrester , etc. I am realistic about what it can do . It is what it is.  One vehicle that you may or may not have owned that would be more heavy duty and more powerful for your needs (boat towing, logging road exploring, hauling more heavier cargo) is the older ford explorers from the late 1990's to the 2001 . After 2001 the explorers just got bigger, heavier and ponderous (and even more expensive). Also the ford explorers are hit and miss with long term reliability ....our japanese suvs are much more reliable then the majority of american vehicles, new or used. Anyways you come across to me as somebody fairly handy and intelligent in terms of vehicle repair and maintenance so that may not be an issue for you. My friend has a 2000 ford explorer, Engine: 210-hp, 4.0-liter V-6, 4dr, 4x4. His father bought it for family duties new or near new and it seems to run pretty good with not too much issues...but mind you, my friend's father is a retired heavy duty mechanic . Even still , i know my friend in recent years needed to drop a bit of cash for wear and tear , maintenance issues, etc. We compared my 06 Xtrail to his Exporer: his explorer sucks backs the gas, strong engine but not as smooth or responsive, the ride is much more stiffer as it is based on a truck ladder/frame, but it can tow a boat or haul heavy items in it's cargo hold. I let my friend drive my Xtrail to compare rides and he was smiling and very surprised how carlike the ride is, how it gets up and goes on the street or hwy, the smooth -comfier ride and the very good long range gas mileage we got on a 500 klm day trip we took. Oh, another vehicle for you that might of been a bit more ''robust'' then the xtrail : the mid 1990's to 2006 toyota highlander. It had a v6 with up to 225 HP in the 3.3L v6 in 2006 and a 3,500 pounds tow rating . They had also a weaker but fuel efficient 4 cyl. , the awd similar to our Xtrails, a very comfortable ride, extremely reliable and very nice to drive. Actually, before i got my xtrail, i had wanted a used 2004-06 Highlander /v6/auto/awd but too many high mileage/ high resale values in my city so i gave up on looking. But if my Xtrail ever gives me too many expensive issues or gets written off, i will continue the hunt for the toyota again. https://en.wikipedia.org/wiki/Toyota_Highlander


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## MikeHJ (Mar 7, 2017)

I will never buy an Explorer again and I've never had a really good Ford product.

The Xtrail was designed to compete with the CRV, Rav4, Forester and Suzuki Grand Vitara.

All 4 had better torque/traction at the low end than the XTrail circa 2000-2006. My friends and I owned one of each. We share driving on a lot of weekend trips so all of them have towed the same boat (not heavy) to the same places for almost 15 years now. There's also a Cherokee, a 4Runner and a Sequoia in the mix, but they are different classes of vehicles.

The Forester and the Xtrail have the best interiors (for useable space and comfort) since they are a touch longer. We find their entry and exit angles about the same: probably scraping the hitch at the boat launch. The Xtrail struggles with the initial pull from a standstill when pulling the boat trailer out of the water and the AWD spins for a second if you have it in auto.

The Suzuki was the best off the pavement, but it isn't a fair comparison in that it had V6 with all the torque below 3000rpm, true 4wd with a low range and a stiff frame instead of a uni-body. It was tighter inside than all the others though, but a little billy-goat otherwise.

The Xtrail is the only one that ground taps over bumps and is generally softer all round. The tranny definitely is geared differently, it has got way worse acceleration than the others and it labors when towing.

I'm keeping my eye out for a Mitsubishi Montero Sport at the moment.


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## quadraria10 (Jul 6, 2010)

All the best for the season guys. Not really trying to enter the debate, but do think it would merit its own thread rather than taking over this one regarding catalytic converter issues.


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## X-hale (Apr 17, 2017)

quadraria10 said:


> All the best for the season guys. Not really trying to enter the debate, but do think it would merit its own thread rather than taking over this one regarding catalytic converter issues.


That's funny, I was thinking the very same thing. Classic hijack.


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## tonyvancity (Jan 2, 2017)

the suzuki grand vitara is also a good choice with the v6 and excellent 4x4 system. Almost bought one new in 2006-07 but the $32,000 price tag was too rich for me.


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## otomodo (May 23, 2008)

So let s stay on topic

If my O2 sensors are showing the same voltage and the second one,sometimes, gives higher voltage. Does that means the catalytic converter isn t working as it should?


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## davidy (Dec 1, 2017)

*Any advice will be appreciated*

My 06 Xtrail with 2.5 engine and auto has 154kkm and has had this P0420 code on 4 times in the last three months or so. When it 

came the first time (Service Engine Soon light was on) I checked the user manual which said that it might be due to the gas cap 

not closed properly, so I checked the gas cap (and to my surpise the gas cap has that warning stamped on it that I never notice 

before) to ensure that it was properly closed and hoping the light will turn itself off after a few trips. A week later the 

light was still there. A staff from the parts store that my son-in-law frequent was kind enough to check it with a scanner and 

told me that it was a P0420 code (and the light was turned off). A week or so later the light came back and as my car was due for 

service, I made an appointment with the dealer shop to have it checked and serviced. But before I sent the car in for servicing 

the light turned itself off. Nevertheless I don't want to get stranded (it is winter) so I have it checked for the P0420 

problem and it costed $82.80 plus GST. The mechanic performed Catalyst efficiency test (I had no idea what that is) and said 

the code did not trigger again but he suspected that the catalyst was starting to plug up (whatever that means). The service 

adviser said that it would cost $2300 to have the three way catalyst (in the engine compartment) replaced which was a lot. At 

the same time the coolant, power steering and rear differential oil need changing too. A few days after the servicing and 

checking, the light came back. So I sent the car in to a trusted garage to get the oil changed (less expensive than the dealer shop) 

and to check out the Service Engine Soon light. I was told not to do anything about the SES light as there was no deterioration in 

engine performance and the lightwas turned off. A week or so later the SES light returned. By this time I have read a number of the 

related postings here (withgratitude) and have just bought a simple obd2 scanner and sure enough it was the P0420 code (the only 

DTC). As the oxygensensors have also arrived (from Rockauto thanks to Quadraria 10 for the link) and the son-in-law has some time, 

he put on the new oxygen sensors and a new set of spark plugs too. The code was cleared. A few days later the SES light was back 

and by this time I have learned a bit about the use of the simple OBD2 scanner and I checked out the freeze frame as well as the live 

data. Voltage of the heated oxygen sensor 1 HO2S1 was between 0.1V to 0.9V and that of HO2S2 was 0.2V to 0.9V (when the engine 

as warmed up) and HO2S2 switched less frequent than HO2S1(no graph was available from my scanner and the data from the 2 

sensors were not in the same screen thus making comparison difficult). I hope that the catalytic converter is functioning properly and 

I (together with the son-in-law who was doing most of the work) will be checking for leakage (air and fuel) and will be looking for a 

gas cap. I am wondering if the Gates 31838 Fuel Tank Cap is compatible for my 2006 Xtrail (linkage into the Amazon screen (thanks 

to Molly) did not even show Xtrail to check for compatibility).


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## chadn (Jan 28, 2010)

otomodo said:


> So let s stay on topic
> 
> If my O2 sensors are showing the same voltage and the second one,sometimes, gives higher voltage. Does that means the catalytic converter isn t working as it should?


Hey Otomodo. They are supposed to show different voltages. The pre-cat one will fluctuate between 0 and 1 volt depending on engine load and fuel-air mixture. The post-cat one will fluctuate between 0 and 1 volts as well but on a different pattern than the pre-cat. 

Do you have a copy of the Factory Service Manual? There is a detailed test procedure that you can do to verify if the catalytic converter is functioning properly or not. You need a scan tool that shows the voltage for both sensors at once. 

Many different issues can cause the P0420 code. The cat is just one of many potential causes.


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## otomodo (May 23, 2008)

When I bought the elm 327 bluetooth, i remember seeing different voltages from both O2 sensors. The first sensor was oscillating between 0v and 9v and the second sensor between 0v and 2v or 3v. 
Now they're showing pretty much the same thing; oscillating between 0v and 8v.
The second sensor, sometimes, shows higher voltage for a few secods. 
Maybe there's nothing wrong with it and it's normal considering the cold weather. 

I have a copy of the service manual. I 'll check the procedure.


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## MikeHJ (Mar 7, 2017)

davidy said:


> My 06 Xtrail with 2.5 engine and auto has 154kkm and has had this P0420 code on 4 times in the last three months or so. When it
> 
> came the first time (Service Engine Soon light was on) I checked the user manual which said that it might be due to the gas cap
> 
> ...


A loose gas cap won't trigger P0420.

It will trigger Evap System Codes, but not P0420.

Sorry to say, but a P0420 code that reoccurs repeatedly after clearing is probably the Cat Converter

They are pricey, but $2300 is way too much. Check out Ultra Exhaust (Ebay store) and find a mechanic to install it


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## MikeHJ (Mar 7, 2017)

otomodo said:


> When I bought the elm 327 bluetooth, i remember seeing different voltages from both O2 sensors. The first sensor was oscillating between 0v and 9v and the second sensor between 0v and 2v or 3v.
> Now they're showing pretty much the same thing; oscillating between 0v and 8v.
> The second sensor, sometimes, shows higher voltage for a few secods.
> Maybe there's nothing wrong with it and it's normal considering the cold weather.
> ...


They should show different readings. It's the differences between the 2 sensors that the ECU reads. The relationship between the 2 is kinda indirect, but they chase each other around to a certain extent. What you want to see is both of them oscillating thru their voltage range with one being faster than the other.

What you don't want to see is one of them getting "stuck" for a few seconds. It is usually a sign that it starting to fail


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## otomodo (May 23, 2008)

MikeHJ said:


> What you want to see is both of them oscillating thru their voltage range with one being faster than the other.
> 
> What you don't want to see is one of them getting "stuck" for a few seconds. It is usually a sign that it starting to fail


They oscillate alright, but 90% of the time it s the same voltage on both or a bit higher on the first( then higher on the second)


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## MikeHJ (Mar 7, 2017)

otomodo said:


> They oscillate alright, but 90% of the time it s the same voltage on both or a bit higher on the first( then higher on the second)


Maybe this article will help. It's for GM engines, but the theory applies to all

o2-sensor-testing


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## davidy (Dec 1, 2017)

​Thank you for the advice MikeHJ. I will keep on observing the behavior of the engine (until my son-in-law comes back to help out) and check out what others have experienced on the subject before taking further action.


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## quadraria10 (Jul 6, 2010)

Whatever you do davidy, don't pay stealership prices to get it fixed. 

Here is some good info on the code as well

The Misleading Nature of the PO42O Code - Eastern Manufacturing

they have a number of good other articles as well.


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## otomodo (May 23, 2008)

MikeHJ said:


> Maybe this article will help. It's for GM engines, but the theory applies to all
> 
> o2-sensor-testing


Thanks
Since the O2 sensors are just reporting the result of the combustion chamber, the second sensor is telling me the catalytic converter isn't doing it's job. 
I ll check that tomorrow when the engine be at a good temperature. 

Thanks again


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## davidy (Dec 1, 2017)

Thanks Quadraria10 for the article on the misleading nature of the p0420 code, very informative.


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## davidy (Dec 1, 2017)

*Freeze frame and live data for P0420*

This is the FREEZE FRAME DATA followed by the live data taken from my 2.5L 4WD automatic 2006 Xtrail. Will appreciate any comments.

DTCFRZF P0420
FUELSYS1 CL
FUELSYS2 -
LOAD-PCT(%) 52.5
ECT(deg C) 84
SHRTFt(%) -3.9
LONGFT(%) 3.1
RPM 2225
VSS(km/h) 88
TP(%) 11.4

live data Jan5
DTC_CNT 1
FUELSYS1 CL
FUELSYS2 -
LOAD_PCT(%)	19.6
ECT(Deg C)	87
SHRTFT(%)	-1.6
LONGFT1(%)	1.6
RPM(rpm) 725
VSS(km/h)	0
SPARKADV(Deg)	13.0
IAT(deg C)	29
MAF(g/s) 1.89
TP(%) 3.9
O2SLOC B1S12-B2S----
O2B1S1(V)	0.100
SHRTFTB1S1(%)	-0.8
O2B1S2(V)	0.13
SHRRFTB1S2(%)	99.2
OBDSUP OBDII
MIL_DIST(Km)	53


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## RangerRay (Oct 10, 2013)

Another silly question: is the smell of exhaust in the cab of the vehicle a related issue to this problem, or would it be something entirely different? I've only noticed it recently especially since our Arctic cold snap that won't un-snap.


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## X-hale (Apr 17, 2017)

RangerRay said:


> Another silly question: is the smell of exhaust in the cab of the vehicle a related issue to this problem, or would it be something entirely different? I've only noticed it recently especially since our Arctic cold snap that won't un-snap.


If there is an exhaust leak in the front section of the system it can trigger the check engine light and code PO420. You could also get exhaust in the cabin, especially while sitting still trying to warm up the car.


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## MikeHJ (Mar 7, 2017)

RangerRay said:


> Another silly question: is the smell of exhaust in the cab of the vehicle a related issue to this problem, or would it be something entirely different? I've only noticed it recently especially since our Arctic cold snap that won't un-snap.


Funny, I've just noticed that too during our -20 cold snap. Just a vague whiff when starting it in the morning, goes away pretty quickly and I don't get it when starting up after work. No other problems and the car runs fine.


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## quadraria10 (Jul 6, 2010)

I do as well some times. Happens also occasionaly when I am at a light behind a bunch of cars. I think its just that in super cold weather exhaust gases don't rise as quickly.Somehow get into fresh air intake. Does not happen often, no codes or other problems. My exhaust is still all original other than a couple of welds.


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## quadraria10 (Jul 6, 2010)

found this
This is actually common....in the cold the exhaust gasses are more prone to hang around at ground level... Ever notice how much steam seems to come out of your tailpipe? Well you heater fan is sucking these vapors into your car thru the cowl of your car. I dont THINK you have an exhaust leak but I could be wrong....you would have to tell us that. If you have no leaks then it IS quite possible that the cold air is keeping those vapors around or near door level...which makes it very easy to suck that air into your cabin.....when it warms up those vapors are far more likely to rise up and away from you...

and

It's the air temperature. Petrol engines need a richer (a larger proportion of fuel to air) mixture in order to run properly when the cylinder head and intakes are cold due to the fuel condensing onto the inside of the intake and ports before reaching the cylinder. The richness is roughly proportional to the temperature of the engine so the colder the engine is, the richer the mixture will be. The excess fuel does not burn completely and ends up as a variety of smelly chemicals in the exhaust.

For modern vehicles with a catalytic converter, there's also a secondary effect where the cat takes longer to reach its operating temperature so more uncatalysed emissions escape out of the exhaust, they smell bad too.


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## otomodo (May 23, 2008)

quadraria10 said:


> The richness is roughly proportional to the temperature of the engine so the colder the engine is, the richer the mixture will be. The excess fuel does not burn completely and ends up as a variety of smelly chemicals in the exhaust.
> 
> For modern vehicles with a catalytic converter, there's also a secondary effect where the cat takes longer to reach its operating temperature so more uncatalysed emissions escape out of the exhaust, they smell bad too.


Maybe that s why my secondary O2 sensor is reading a higher voltage. 

Are you using a plain paper air cabin filter or a carbon type?


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## quadraria10 (Jul 6, 2010)

carbon type


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