Help to trace the problem P0174/P0171
Thread Starter
TECH Regular
Joined: Jan 2002
Posts: 462
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From: Austin, TX
Help to trace the problem P0174/P0171 My SES light keeps coming on and goes off in a day or two (when I put my AC on it goes off sooner). I am puzzled! The B1 stays @ 23.7 and B2 stays @ 19-20. I have no idea why this is happing! It throws a code P0174/ and P0171.
About 4 weeks ago I checked it and P0153 code was there too. I don’t have that code (P0153) anymore but these P0171 and P0174 keep coming and going! Is it possible because of the cold weather? Do these codes hurt my WOT performance? Is there a way to fix this problem? Any help is greatly appreciated! Would it be ok to delete theses codes by LS1Edit?
This problem started about a week after I installed my NX MAF and the cat-back. Could it be a vacuum leak?
Thanks!
About 4 weeks ago I checked it and P0153 code was there too. I don’t have that code (P0153) anymore but these P0171 and P0174 keep coming and going! Is it possible because of the cold weather? Do these codes hurt my WOT performance? Is there a way to fix this problem? Any help is greatly appreciated! Would it be ok to delete theses codes by LS1Edit?
This problem started about a week after I installed my NX MAF and the cat-back. Could it be a vacuum leak?
Thanks!
TECH Addict
Joined: Jun 2002
Posts: 2,428
Likes: 0
From: Las Vegas, NV
Re: Help to trace the problem P0174/P0171 Those codes are telling you that you are very lean, beyond the pcm's safety net of +25 LTFTs. It sounds like your new maf put you over the top. If you simply put your stock maf back on, you would bring those LTFTs closer to zero. Also, I noticed that you did an egr mod: it's very common to develop a leak at the manifold which would cause your LTFTs to be so lean. I would check for an egr leak first, and if that checks out okay, I would put the stock maf back on.
Re: Help to trace the problem P0174/P0171 BOTH LTFT and STFT have to be over the limit (either both pos or neg) for the code to go set. Just one or the other over the limit by itself won't do it. I think the limits are 23% AND 5% for LTFT and STFT respectively. If this happened after a mod you know that mod had something to do with it. As you were just told look for a vacc leak and it doesn't take much. If you did an EGR mod you need to look closely at where the EGR tube goes into the intake. That's a source of an air leak that won't be measured by the MAF to send you lean which the PCM will try to compensate for by adding fuel sending your LTFTs and your STFTs way up on the POS (+) side percentage wise. If you have a leak in the plenum between the throttle body and the MAF this will also send you lean and result in a POS fuel trim reading and eventually set the code. Go back over your work and look for a place for air to get in (even something tiny can make a difference over time). All mating surfaces must be tight and flush to seal properly.
