Hello everyone, just joined the thread.

I am posting due to the infamous P0171 code. Lean long term fuel trim.

I have had this problem for about a year or so. First time i took it to the dealer, they said there was a software update available to fix the problem, so that was done under warranty. The problem still kept on happening, so i took it back as soon as i had the chance (about two months). That time they said the AFM was sekwed high. Again, replaced under warranty. Problem still keeps on happening. It's been about six months or so since then. I was on a trip to NY and the MIL came on again (not surprising), so I had a friend of mine check it out with his scanner. here's the gist of what was going on:

Engine Temp: 180 Degrees
Engine load: around 15-20% i believe
Vehicle Speed: 74 mph
Long Term Fuel Trim: +28

that's what i can remember from the freeze frame. The car holds a consistant vaccuum when on the highway, usually about 12.5 inches of mercury. Of course, that does change on the hills. Coolant never gets hotter than 181 on these trips. Fuel mileage is 34 and some change. He kept poking around this time with the car on. he looked at the MAF, and all looked fine with that. Then he looked at the H02S's, both up and down stream. The upstream sensor was working normally, bouncing around 760mV, moving up and down nicely. The downstream sensor was literally stuck at 1V (yes, regualr volt, not mV). It wasn't budging at all when he would tap the gas. just stayed at 1V. His best guess was the downstream O2 was lazy/busted. So i picked one up, threw it in, and drove back to Ohio. Light came on again. HOWEVER, the light comes on only when I do the following:

On a long trip (such as driving from Ohio to NY), I fill up the car and go. All is fine, now it is time for gas (i usually stop when i have 1/4 tank left). I fill her up and go. EVERY time, within 5-10 minutes, the light comes on. The real kicker is that just by driving around town for a day or so, the light will go off. It isn't just stop and go, but also short hops on expressways and such.

It's confusing how for the entire first tank of gas, the car is fine. Only after the fill up does she trip. And, this happens EVERY time. I am unsure exactly how much gas i have to burn on the expressway, it's just habbit that i fill at 1/4 tank on the road. It has happened a couple times driving out in rural country side, stopping to look at something, and then going again, but, hard to get it to repeat....

I took her to the dealer before i even got home yesterday (the dealer is right around the corner) so they could see exactly how the car was running at that point in time, which is what they told me to do next time it happened (a few months ago). So, i left it with them, and they took me home. They called me this morning, noticing the new 02 sensor, and said they couldn't find any record of another GM dealer performing the work. I told them that I did it, and that i did not have the original sensor with me. The short of it is that they will not warranty anything without an OEM sensor in it, and they want $187 for a new sensor. No way!!! I called my buddy to see if the old sensor was still on his tool box, and it was. So, i have to have him mail me the sensor, put that sensor back in, take it to the dealer again, and then they will warranty what needs to be warranteed (they better stick to their word on that.....)

I post this because i have a hard time believing that the new sensor would output exactly the same way that the bad sensor did. I know, it is possible to have a bad sensor, but, with the exact conditions as the previous, I think it's kinda slim.

I should also add that the car is box stock, no mods other than the warranteed software update (was NOT the stage reflash).

Engine vaccuum also acts fine. That is, in neutral, jab the gas pedal and it goes to zero, and falls back down just as it should. no weird fluttering or anything like that indicating mechanical problems inside the valve train, or a plugged up cat.

The car also drives completely fine the entire time the code is on.

Before i replaced the sensor, she had a weird hesitation under partial throttle. hesitation is the wrong word, but i can't think of a better word to use. just accelerating normally, with approx. 5psi of boost, it just felt like a flat spot or a hole in the fuel curves. no real shudder or shake or anything like that, just a split second pause like it was confused and wasn't sure exactly what to do. that part make any sense to anyone? With the new sensor, that issue went away, which would make me think that it's not the sensors problem.

man, that was kind of an essay, but, wanted to be sure to dump as much info as possible instead of some of the vague postings. I will be checking the entire intake system tonight when I pick it up from the dealer. I'll look at all the vaccuum hoses and connections, spray them with some carb cleaner and see if the rpm's rise confirming a vac leak. i'll also look at the intake ducts and AFM mounting to see if they are all ok. same with EVAP lines, and gaskets on the intake side....

ok, enough of the essay, anyone have any other ideas????

ok, just got back from the dealer, i also got more codes this time....

P0171, which i knew would be there
P0141, 02 sensor heater performance
P0172, which is long term rich fuel trim... interesting....

any takers?

 

no ideas from anyone??? i know this is a problem with everyone it seems, but, is there nothing i can do? or am i just wasting my time?

 

They cannot force you to replace the O2 sensor with a GM part, the Magnuson-Moss act was put in place for this exact scenario. However, if the O2 sensor was under warranty you should have had them do the work under warranty anyways.

 

I agree with rnjmur...ya should have let the dealer do it.....but to your problem....I had that pop up after I installed my clutch....mine was thrown due to a kink in a vacum line....what I would do is disconnect the batt.....remove the fuse box/PCM/ the vacum line to the brake booster/ throttle body and...unplug the one that runs to your intake to the engine.....let it set for a day or two....reinstall everything....and see what that does....if it still comes up....wire harness short maybe???

 

Your sure they reprogramed with the calibration for the P0171 code ? There are alot of things that can set this ....I'll copy the diagnostic from GM over later . Basically it said dirty injectors ...injector O-rings .... Dipstick sucking air .... loose air intake ..... supercharger manifold gasket ...... fuel pipe , plugged fuel filter , weak fuel pump.....list goes on .

 

schluterdude did you ever resolve your issue? I am having very similar problems with my 06 2.4L SS. (Check engine light turns on after filling up on long drives and turns off after in town driving, etc) I just had my injectors flushed, drove 340 miles on the interstate and it did the exact same thing. I ran a code search and my car pops out a P1174 code. After a little searching, it appears it could be a number of different things, no surprise. Not sure what I should do to resolve this.

 

ok....I had my schools engine performence calls recalibrate my ECU...evedently there is an update and they said tha tI need it....had it done wensday....so for so good....if it comes back on I'm replacing the upstream HO2 and MAF sensor....since the upstream one is what changes the A/F ratio....if I get anyo ther issuses....I'll pass it along...