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amb4081

CEL...P0171 and P0174

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Checked the ECU for the P0171 and P0174 trouble codes. They are Bank 1 and Bank 2 running lean. Does anyone know what could be causing or where I should start looking at for the source of the problem? Or is this something the dealer should deal with? Thanks.

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amb – It could be that both o2 sensors are bad. That is what happened to my 2001 pathfinder. Another thing you might want to check on is getting your computer updated. It will cost you $70 but may be worth it. The reason I say this is because from 600 miles up to 38,000 miles I had replaced both left and right rear O2 sensors and my Valve Timing Sensor. When they replaced my last O2 sensor I told them that I heard you could update the computer and that this might help. Well I’m at 53,000 miles now and have not had a problem since they updated. It kind of made me wonder if they really had to replace the VTS and the O2 sensors. It could have saved me some $$$ if I did the update first. I’m not saying that this is your problem but it is something to think about.

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Thanks for the info. I'll check into that and talk to Nissan probably about it. It just puzzles me that the ECU will spit out the PROBLEM but not a component that has failed or is triggering the listed trouble codes.

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It just puzzles me that the ECU will spit out the PROBLEM but not a component that has failed or is triggering the listed trouble codes.

That's what the factory service manual is for. For those two error codes there are many possible causes including:

 

Intake air leaks

Front heated oxygen sensors

Injectors

Exhaust gas leaks

Incorrect fuel pressure

Lack of fuel

MAF

 

The codes tell you its running lean, but you'll still need to investigate what is causing it.

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I can see if intake or exhaust leakage or even injectors are a cause. But my experience in the past is if an O2 sensor or other component FAILS, the ECU spits out the trouble code for that particular part, not just what is happening because it fails.

 

Also, to note...I reset the CEL the first time it came on. It took about two days to come back on. Then I reset it again. It came on within a few minutes of driving after that. There does not seem to be any loss in horsepower though, no hesitation at all versus when we first bought it. The fuel economy is slightly less which leads me to think possibly O2 sensor(s). But I'm just surprised the O2 sensor code didn't trip.

Edited by amb4081

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You don't happen to have an aftermarket filter that uses oil do you? The two codes are most commonly traced back to an over oiled filter and the oil coating your maf wire (or a dirty maf wire).

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No. I just used your typical STP or Fram oil filter. I think this one is STP. I've used them in the past and never had issues before.

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But my experience in the past is if an O2 sensor or other component FAILS, the ECU spits out the trouble code for that particular part, not just what is happening because it fails.

In this case the diagnostic procedures for P0171/P0174 are not checking to see if the O2 sensors are bad, just if the connections are OK. You're right, if the O2 sensors were bad you should get O2 sensor errors. For these error codes it has you check O2 sensor harnesses for continuity on specific terminals.

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No. I just used your typical STP or Fram oil filter. I think this one is STP. I've used them in the past and never had issues before.

I meant air filter. K&N style air filters need to be oiled. If you over oil it or drive it right after its been oiled you suck the oil through it and it coats your maf wire. Then besides being covered in oil dirt sticks to it. Then the maf can't properly register the air coming in which causes a lean condition, which trips codes p0171 and p0174.

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Oh. No. I just installed the throw away cartridge type.

 

Could a "bad" tank of gas cause something like this?

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I guess a bad tank could do it? Run it out fill her up and reset the codes and see if they come back. I am still pointing to a maf problem. You know anyone you can swap mafs out with to see if the problem goes away? In the car world these are very common codes and I would say about 85% of the time have to do with the MAF. Good luck!

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Ok. I'll give it a little time to work out some. Thanks for all the replies. I appreciate it.

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