# DTC Codes - Knock Sensor & Vacuum Cut Valve Bypass Valve



## hawaiibrew (Sep 14, 2005)

My 2000 Frontier Club cab recently had the "Service Engine Soon" light come on. The car has been running fine..no problems at all. Only 37,000 miles.

I bought a Innova 3030 OBD2 reader to try and find the problem myself.

I got two codes

Nissan DTC 1491 Vacuum Cut Valve Bypass Valve

&

Nissan DTC 0325 Knock Sensor 1 Circuit Malfunction

The 1491 I'm not too concerned with unless it's leaking gas...which it's not. Nissan has posted a Service Bulletin for this problem...hoping the dealer might replace it since it is emission related.

The Knock sensor seems funny since the truck is running great.

I'm guessing that the sensor itself it not working properly and is not responding to the ECU when the ECU is trying to contact it.

Anybody replaced a knock sensor on a 2000 Nissan Frontier or similar?

Dealer is going to want $$$$$$ to replace that sucker!!

The part alone is around $120.

Anyone know of a problem with deleting these codes? Possible that I hit a bump in the road and it triggered the 1491 error?


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## hawaiibrew (Sep 14, 2005)

*Deleted Knock Code and 1491 code*

After much reading and researching - it appears the 1491 code is related to the EPA system which recaptures gas vapors and reintroduces them into the engine for burning.

Since I live in Hawaii and we have no emission standards I deleted this DTS code. Possibly some blockage in the tubes caused the error or water, or (I did overfill my tank a little the day it came on).

As for the knock sensor....from what I read - the knock sensor in Nissans will help sense when the engine is knocking...

but Code P0325 refers not to bad knocking..but to a failed knock sensor itself.

The error could be caused by a bad sensor, wires that have come loose to that sensor, or a problem with the ECU.

But if the truck is running normally, the bad sensor is not a direct threat to your engine.

I expect to replace it in the next couple of months when I have time, but the truck is running great right now and I think it can wait a little while till I have time to get under the intake manifold.

If anyone has replaced one of these though I'd love more info on the procedure.

Mahalos!


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## rps180 (Aug 20, 2005)

As for 1491, there is a TSB for it, but unless your truck is still under warranty you won't get a free replacement. TSB's aren't recalls, just a bulletin for tech's to go by in case they come across a known/common issue.

Knock sensor replacement isn't easy. The entire intake manifold will have to come off, and it isn't easy to get it off. The hardest part will be removing and reattaching the heater hose lines that are attached behind the manifold. You will definitely need some sort of extended reach pliers to get the clamps off. Then you will need either slim hands with a strong grip, or extended reach hose pliers to pull off the hoses.
If the heater hoses look a little cracked, now would be a good time to replace those as well. Also, there are two vacuum lines at the back of the manifold. Might be a good time to replace these as well.
Also, don't forget to order a new intake manifold gasket. You will need to replace this when you put back the manifold.


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## hawaiibrew (Sep 14, 2005)

Yeah the truck isn't under warranty so I'd either have to do it or pay someone to do it. I have no problem with doing it myself, just don't have a place to work on it.

As for the 1491..like I said, we have no emissions requirements in Hawaii and since I don't think the DTC is regarding something that would effect performance I'm going to skip out on that one for as long as I can (just have to deal with the light being on for a while)

As for the knock sensor....since it isn't a huge deal right now..I'll wait until I have a garage or carport so I can take things apart and I'll do it myself.

Thanks for the help....gonna order the knock sensor ..found em on ebay for $60.

ALso got the 1500 page factory manual on CD ordered


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## gritz138 (Oct 12, 2004)

*knock sensor info*

I'm working on a knock sensor fault on a 2000 Frontier as we speak. Was hoping to find some helpful hints on here to save me some trouble. Tried tracing wires to see if I could unplug something and test the resistance on the sensor prior to removing everything, and it doesn't seem possible.

You guys have only confirmed the issues I'm seeing right now. Will have the intake mainfold off tonight. Got the top section apart yesterday evening. So far all info posted here is exactly correct. The hoses, vacuum lines and wiring are extremely difficult to remove.

Really nasty place to put a sensor.


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## rps180 (Aug 20, 2005)

Even if there were another remote section you could test the sensor from, unfortunately, it is one of those things where 99% of the time the knock sensor itself is no good and requires replacement. But, you could attempt to check the knock sensor from the ECM harness.


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## gritz138 (Oct 12, 2004)

I'm finished now. It was the knock sensor. Got the new one in, gas mileage is already up. It was an evening to get it all apart and an evening to put it back together. Big hassle for such a small part. I put the new one back in the same spot but now that I know the wiring path to the sensor the next time it fails (if it does - knock on wood), I'm cutting the wire at the back of the manifold and installing the new one somewhere else.


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## hawaiibrew (Sep 14, 2005)

*Gritz*

Hey..I'm going to attempt this next week sometime once I have some space to work on the truck.

How long approx did it take...were there any difficult tricks to removing the manifold?

Where did you buy the knock sensor at? How much was it?

If I take some pictures of my engine..would you be able to point out where the knock sensor is located and the easiest way to access it?

I'll send you a private message with my email..many thanks!


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## gritz138 (Oct 12, 2004)

I sent a more detailed message to your private message.

Take apart 3 hrs.
Put back 4.5 hrs.

As far as the picture, you can't miss it after you get the whole manifold off. Should also show you in a manual. The torque requirements are really low on all this stuf and you'll need the manual for that info too.


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## hawaiibrew (Sep 14, 2005)

*Part number of 2000 Nissan Frontier Knock Sensor*

What was the Part #? I was getting dicked around by my dealer and they wouldn't tell me what the fricken part number is.

THanks.

Brew





gritz138 said:


> I sent a more detailed message to your private message.
> 
> Take apart 3 hrs.
> Put back 4.5 hrs.
> ...


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