# 2010 altima 2.5 p0420



## 2010altima (Jul 27, 2016)

My wifes car has the p0420 code. Watched the o2 sensor readings and both 1 and 2 are fluctuation up and down. I know sensor 1 should fluctuate and sensor 2 after the converter should stay steady if the converter is working right correct? I took the shield off the manifold and there is yellow stuff all over it. I dont know if its cracked or anything but where did the yellow stuff come from? Car isnt running rough good mileage everything seems fine but that code is well know for converter failure. Just wanting some input on this.


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## 2010altima (Jul 27, 2016)

Here's the yellow stuff all over the manifold and converter. Is it cracked letting this out of the converter? Couldn't see anything on the front side so maybe it's on the back?


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## Car guy (Mar 31, 2016)

Has the engine been burning oil? How many miles?

Do you have an infrared gun?

What do the FTRMs show? Running rich?


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## 2010altima (Jul 27, 2016)

Not really burning oil that I've noticed. Just on long trip on the interstate. Car has 104,xxx miles and yes I do have a infrared heat gun. I watched the o2 sensors on a Snapon verus scanner and the front sensor is going up and down like it's supposed to and sensor 2 is doing the same. I was told sensor 2 after the converter is supposed to straighten out not be jumping up and down like sensor 1.


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## 2010altima (Jul 27, 2016)

Sensor 2 was showing lean when watching the scanner.


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## Car guy (Mar 31, 2016)

> I was told sensor 2 after the converter is supposed to straighten out not be jumping up and down like sensor 1


That is somewhat correct. The downstream (S2), once cat is at operating temps and its heater is running, should have a slower switching cycle than the wideband (dual) AFR (S1) (upstream). But, it should still switch: between rich (.68 +/-) and lean (.1x +/-), depending upon the engine operating performance (accel/decel/fuel cut/et al). So, a lean-showing S2 is okay. A chronically lean S2 would not be. But, the ECU through the S2 is measuring the cat's oxygen content for its performance/efficiency. So, a chronic lean in your case would seem unlikely, unless there is a continuous engine air in-leak or exhaust leak or the heater circuit or the S2 (zirconia) itself is failing. 

The previous gen Altimas did have significant exhaust/cat issues; so, you are correct on that - history-wise, and with your code; but, haven't seen that same issue on your gen (though your gen is known for exhaust manifold/cat/front pipe weld and rust prematures).

The FTRMs would tell us more about whether the cat may have become contaminated or clogged. If they (short and long) are very negative, that could be a telltale. Raw fuel takes out cats. Oil burning over the miles can too. I would be surprised if yours has not been burning oil, but it is possible. 

At your mileage, have to ask, have the 105k-mile-rated spark plugs been replaced? Slightly fouling, contributing to your condition/code. When (& what mileage) were they replaced?

Also, a leaking injector could relate/cause your situation. Also, an air leak (undetected by the MAF, beyond that point) (or at any exhaust boundary) could relate.

Also, take your thermal gun, get the car/cat fully operating temp hot, keep it running, aim just before cat and just after cat and aim at beginning of cat and at end of cat; both afters should be hotter than befores. What do you read in doing these thermal checks?

Also, your S2 sensor is a heated sensor (for emissions efficiency), so checking that circuit (those 2 wires of the 4) to ensure it (that heated circuit) is operating could be done, assuming no air leaks exist and assuming the plugs have been replaced recently (and with OEM/NGK). No sense replacing the cat if the issue is wiring to/from the S2 sensor or the heated circuit therein. Though I doubt it is your wiring because there are separate S2 MIL codes for those conditions.

On previous gens, for cat problems and your code, Nissan had TSBs for disconnecting the exhaust gaskets, replacing them, and visually checking the insides of the cat for holes or clogging. 

If you could capture LIVE ECU data and post it here, various folks could assist further.


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## 2010altima (Jul 27, 2016)

Here is a screenshot of what the front sensor is doing and the rear sensor after the cat. Tells the highest point and lowest point. I'll try the heat gun see what the temp is of the cat. So the temp before the cat should be lower than the temp after the cat?


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## 2010altima (Jul 27, 2016)

Might I add there is no other code besides the p0420. No oxygen sensor codes or anything. The car runs fine no rough idle missing. No horrible fuel mileage nothing to that nature. Just the yellow crap all over the manifold and converter is what has me confused. I seen where a guy had an 08 and had the yellow stuff all over and he had a crack in the converter next to the motor. I haven took mine off to check for cracks. Couldn't see any when I took the front shield off. Everyone is saying the converter is failing or has failed with this code coming up. Seems to be a common problem on the 2.5s.


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## 2010altima (Jul 27, 2016)

Yes the plugs were just changed with oem Nissan ngk plugs at 100k. The old plugs look fine not white chalky good burn from the plugs. Car runs fine seems like to me.


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## Car guy (Mar 31, 2016)

> Might I add there is no other code besides the p0420. No oxygen sensor codes or anything. The car runs fine no rough idle missing. No horrible fuel mileage nothing to that nature. Just the yellow crap all over the manifold and converter is what has me confused.


Yes, I saw (and took into account) how there appear to be no other issues and how performance appears fine. Had looked at the pics also, but couldn't make out the extent of the yellow.



2010altima said:


> Yes the plugs were just changed with oem Nissan ngk plugs at 100k. The old plugs look fine not white chalky good burn from the plugs. Car runs fine seems like to me.


Excellent (new ones). Great (old ones). That should rule out any fouling that would have added fuel to (damaged) the cat. You say good burn on the old ones; were they carbon'd up/over at all?

Burning/consuming oil also hides issues and leads to car seeming to run fine. Not trying to belabor this point, but have seen a lot of oil consumption (quart per 3000 mile change interval). Hurts cats.

Now on your data, thanks for including that. It all seems normal, except that the S2 cycle time seems delayed/drawn out. I would have expected to have seen 5-second cycle times, not 10-second. The S2 peak to peaks seem normal, themselves. Car was idling and at normal operating temps. MAF rate seems normal. Delayed/drawn out S2 cycle times are consistent with reduced oxygen content in the cat, and your code. The cycles delay as the cat fails. I would prefer someone else also weigh in on the cycle durations of S1 and S2, before condemning the cat, especially since something else usually causes it.

Would still like to see the car's fuel trims (STRFM and LTFTRM).

And, leaking injectors still could cause premature cat failure.


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## 2010altima (Jul 27, 2016)

Thanks for all the help. The yellow stuff is all over the manifold and cat. There was a guy with the 08 had the same stuff on his and the converter was cracked on the back side toward the motor. That exhaust leak could cause the p0420 correct? Called Nissan about a recall on the ecm reprogram and converter issues this car doesn't fall under the recall. Think I'm going to order a new manifold and cat and install it and see if that takes care of it. 

I've cleared the code a couple times before and it does take it awhile like a month for it to come back on. Getting ready to take a 12 hr trip in it and wanting to try and figure this out. 

Won't be able to hook the computer back up here at work so won't be able to get the fuel trims just yet. Wife's working and driving the car.


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## Car guy (Mar 31, 2016)

2010altima said:


> Thanks for all the help. The yellow stuff is all over the manifold and cat. There was a guy with the 08 had the same stuff on his and the converter was cracked on the back side toward the motor. That exhaust leak could cause the p0420 correct? Called Nissan about a recall on the ecm reprogram and converter issues this car doesn't fall under the recall. Think I'm going to order a new manifold and cat and install it and see if that takes care of it.
> 
> I've cleared the code a couple times before and it does take it awhile like a month for it to come back on. Getting ready to take a 12 hr trip in it and wanting to try and figure this out.


You're most welcome.

Yes, sure would cause it. And, yes, all this is all consistent. Nissan did have a recall for some VINs, but then ended that for all the rest (of us).

Nissan did change parts. There is a new superceded part. In fact, there was a new part for the earlier cars in this same model gen (the ones that covered the other guy's '08). Two integral-exhaust-manifold/cat parts each needing new parts, within the same gen! Four total exh/cat parts. And, still the recall/warranty was not extended.

Interesting you mention the '08 with cracking on the rear, as that is hard to spot. Consistent also, as the ones I've seen on the front are developing circle rust areas but not pin holes or cracks yet. But, they are getting there.

You're getting a new exhaust manifold gasket and bottom flange gasket also right? And, new OEM stud nuts for top and bottom?

Should ask also: how are the front and rear heat shields looking? Rusting? They have different bolts for front and rear shields. And, interestingly, each of those bolts also have superceded. Had to replace our shields and bolts already, due to premature rusting. (Nissans have rust and CVT issues.) The shields have built-in mesh screens as buffers between the bolts and the actual shields (at each hole). This helps some.

Let us know what you find and how you make out. 

It also would be helpful to see the same graph data under the same conditions once you're remedied (code gone).

P.S. If the FTRMs end up looking okay and the engine oil level is not low, then you're likely on to it (via the obscured backside crack).

Oh, and one other thought, relative to the FTRMs. Under normal operating conditions, the downstream S2 is not used by the ECU for injector pulse control. But, if the upstream is ajudged problemmatic, the ECU will, under those circumstances, try to use the S2 to maintain stoichiometry (AFR). I doubt this is happening, but useful to keep in mind.


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## 2010altima (Jul 27, 2016)

Yes getting all new gaskets and bolts studs. The heat shields look like new no rust or anything like that. I guess I'm going to order the one this weekend and see what happens. Thanks again for the information and help


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