Code PO171

[Mooseknuckle]

Ok I had a new PCM tuned from PCM4less. Put the PCM in and went to dealer to get the crank variation relearn(57.27 with tax) I still have the PO171 code. While I was waiting for the pcm to return to me I cleaned the throttle body and gutted the air box and replaced air filter with one from Amsoil. I dont have any stall issues but the truck cyles through 900 and 1100 rpm's. I went to Autozone they told me it was an oxygen sensor. There are four sensors, is the PO171 the MAF sensor? can I just pull it and clean it or is there something else I should be looking at like fuel filter or fuel pump or vaccum leak? How do you clear the codes,scanguage?

[Trail X]

http://www.offroadtb.com/articles/tech- ... tic-sheets

Looks like P0171 could be an O2 sensor, however it looks like P013X and P014X are more common O2 sensor DTCs. P0171 seems to imply you're running a lean condition. Do you have a rough idle? It could either mean you're not getting adequate fuel, or that you have a vacuum leak - although a faulty O2 sensor could always be the culprit.

[Mooseknuckle]

http://www.offroadtb.com/articles/tech-docs/engine-and-transmission-diagnostic-sheets

Looks like P0171 could be an O2 sensor, however it looks like P013X and P014X are more common O2 sensor DTCs. P0171 seems to imply you're running a lean condition. Do you have a rough idle? It could either mean you're not getting adequate fuel, or that you have a vacuum leak - although a faulty O2 sensor could always be the culprit.

Its a slightly rough idle reving or cycling between 900 and 1100 rpms but never stalling. another words its not constant on 1100rpms. I have the print out from autozone. Since I havent had this problem until I cleaned the throttle body and recieved a NEW pcm i thought it could be the pcm. I dont know where engine bank 1-2 are. I guess i will start with the maf sensor,then the O2 sensor ..if its the O2 sensor I'm thinkin of they are like 150.00 here is the print out:
fuel trim bank one condition
explanation
the pcm uses O2 sensor to calculate the air/fuel ratio of the engine.the computer has recognized a rich or lean condition on one engine back only.
probable cause
if bank one and two codes set together suspect fuel pressure or maf sensor
oxygen sensor defective
ignition misfire-repair
fuel injector problem.

[Trail X]

Your engine is the I6, right? You only have 1 bank.

To me, it sounds like you have a vacuum leak.

The result is that you're getting extra air into the engine that it's not accounting for... so the fuel amount delivered is calculated for lower RPM and less air, thus it's running lean (not enough fuel) and at a higher RPM (not enough vacuum).

[bgwolfpack]

Certainly sounds like a vacuum leak of some sort. Your idle is too high at 900-1100 rpms. The engines resting idle should be around 600 rpms.

This could also be the computer stuck in the warm-up cycle. What does the temperature gauge say? Do you have a scanner? High idle can be caused by an open thermostat.

[Mooseknuckle]

ok so i have to hook a vaccum gauge up..dumb question..does it tell you where the leak comes from? or do you find out by the built up pressure,never used one before. I was wrong its cycling from 600-800 rpms 900 when I first start. I hear something off around the maf sensor almost like its leaking air hard to completely pin-point due to the engine being on but to me that where it sounds off..next step?

[Trail X]

http://www.aa1car.com/library/vacleak.htm is a good reference. I use aa1car.com a lot.

To me, the most obvious culprit is the top hose on the throttle body (since you just cleaned it). Make absolutely certain it's secured properly. I've had trouble re-seating that hose before and it could be your problem. Make sure all of your hoses are properly connected to your intake, there are a few accessory vac hoses that come off the right side of the plenum.

However now that you say it's cycling from 600-800, my next question is - did you reset the computer after cleaning the throttle? Leave the battery negative connection disconnected for 30 minutes. It should allow the PCM to forget it's prior trim calculations for the throttle body. Once you clean the throttle body, it has to re-learn the correct valve position in order to idle properly. A surging idle could point to needing a memory wipe.

[Mooseknuckle]

no i dont think i did that..but here is my next question will i have to do a crank relearn or secruity relearn after having the neg from the battery off for that long? I was actually goning to retake everything off again to see if i did it right and to make sure everything was secure..thank you James great idea!

[bgwolfpack]

no i dont think i did that..but here is my next question will i have to do a crank relearn or secruity relearn after having the neg from the battery off for that long? I was actually goning to retake everything off again to see if i did it right and to make sure everything was secure..thank you James great idea!

Great idea! No, you do not need a relearn after disconnecting the battery. The info is set to the PCM.

BTW yer killin me spill cheker!

[fishsticks]

Start your engine. Grab a can of starting fluid (WD 40 works, but leaves a mess) and spray it around the connections for your vacuum lines. If the idle suddenly changes when you spray somewhere, you've found your leak.

[jpfeffer]

For what it's worth:

I had an Audi TT that I bought with a CEL on and P0171. I drove it for close to 8 months with that light on because I couldn't figure it out. I joined an Volks forum and went on a cruise with them after 8 months, and the night before, I went to Autozone for a few cleaning supplies, and since I have a rewards card, I went ahead and fell for the "Buy a Bottle of Injector Cleaner" at the counter since it put me above the $20 limit to earn a "point". Didn't buy it intentionally is what I'm getting at. I put it in the tank and filled up (it was with Premium, since the TT is a turbo 4 cyl, in case it matters for anyone reading this). I went out the next day on the cruise with the VW guys and met up with a Ferrari and my build TT was the fastest car in the group (still no Ferrari), so we were getting on it pretty hard down some back roads, and after around 3 hours of very heavy driving, I was at the last stoplight before my house and when I took off, I got on it one more time and it fell on it's face, the CEL flashed like I had a misfire, then I regained power, the CEL went off and it never came back on Had it inspected and it passed and was good after that until I sold it.

Over the 8 months of struggling to find the cause (without paying the dealership), I was told by countless people it was FOR SURE a vacuum leak, or it was my K&N taking in too much air for the fuel pump to keep up. I switched to a stock airbox, didn't help. Sprayed around the engine for leaks, didn't help. Was on the verge of switching to all silicone hoses and a bottle of fuel injector cleaner and some aggressive driving fixed it. I've always assumed it was a clogged injector or fuel line causing not enough fuel to make it to the engine and when it "fell on its face", it cleared the blockage. This is just my experience with this code though. It was incredibly frustrating. Maybe this will help either you, or someone else down the road who is plagued by the P0171.

By the way, after telling this to a few people, one of them had been a dealer mechanic for years and years and he said that was the common "fix" for lean conditions. Fuel injector cleaner and "spirited drives" in a customer's car. Take it for what it's worth. He was obviously crazy enough to work for a stealership for years....

[Trail X]

BTW yer killin me spill cheker!

For real!

[Philberto]

Had the same code, turned out to be a MAF sensor for me... But then again, I've got an '06.

-edit: And so do you! Worth a look-see and maybe a run to the junkyard for a salvage part.

[Mooseknuckle]

BTW yer killin me spill cheker!

For real!

LOL I know i know I know. I will spell it right now,security, there we go. I was rushing,at least that is what I'm going with. Fish great idea,thank you,I spoke with a friend of mine earlier said to do the same thing. I've been at work since 1:30 pm and am working overtime till about 7am friday morning then straight to the shop for an alignment,then home to shower and pass the F out. When I awake from the dead I'm gonna spray everything first see what happens then i will re-check everything and disconnect battery. If all else fails I will get a maf sensor. Thanks guys I appreciate it.

[Mooseknuckle]

Little update. I got the engine light to go off. I took your advise James and disconnected the neg from the battery for about 40 minutes and took everything apart. I cleaned the back of the throttle body where the screws thread into that had residue build up all over it . cleaned it up put all back together. re-connected the battery started the truck and no engine code. Drove it around for a bit good to go. I also bought some MAF sensor cleaner and cleaned the hell out of it. Anyway thank you.

[OregTrailBlazin]

Start your engine. Grab a can of starting fluid (WD 40 works, but leaves a mess) and spray it around the connections for your vacuum lines. If the idle suddenly changes when you spray somewhere, you've found your leak.

I like to use Propane, I use a small piece of rubber hose over the end of one of those little torch's, works great, and isn't as bad for the engine as starting fluid....

[Mooseknuckle]

Ok I had the engine light off now its back on. Had another scangauge read the same code po171 bank 1 o2 sensor too lean. I sprayed starter fluid throught the engine and heard nothing change. I removed the MAF sensor and sprayed the crap outta that and put it back in place. I had the battery disconnected and took apart everything to the throttle body and step by step put everything back in place to ensure fitment. Looked good. reconnected battery engine light was out,hour later back on. I know there is upstream o2 sensor by the manifold and a downstream 02 sensor by the cat. Should I start with the upstream since the scan gauge said too lean o2 sensor ? i have also noticed once in a while the exhaust smells like it is burning but that goes away as soon as the engine warms up a bit. Also would getting a CAI help, probably a stupid question but it eliminates the MAF sensor? Thanks guys

[Mooseknuckle]

I was just looking around and kept seeing throttle body gasket. Her is the next question when you take off the throttle body is there a gasket that needs to be replaced when putting it back after cleaning it? I dont remember seeing one.

[fishsticks]

I was just looking around and kept seeing throttle body gasket. Her is the next question when you take off the throttle body is there a gasket that needs to be replaced when putting it back after cleaning it? I dont remember seeing one.

There's a gasket....but it's basically part of the intake manifold. It's reusable.

Replaced the O2 sensor yet?

[Trail X]

That might be the next logical step. At least you'd eliminate it as the issue.