Hey all - I am trying to sell my 2008 LT w/121,000 miles - the thing is in great shape, and I have taken what I believe to be excellent care of it. New tires, brakes, rotors, plugs/wires, starter etc etc all to get into tip top shape to sell......
It has a P0172 code..... it comes and goes (sometime I get in the car, no check engine light). But it is on now, and that is a big issue for me trying to sell it.
So I brought it to a mechanic I know, and he sprayed cleaner into the sensor coming off the air filter, and we ran engine cleaner through the top of the engine (what a fantastic smell that smoke has btw).....
The code still came back.
I have put so much money into the car to get it ready to sell - and I feel like I am going down a sinking ship.
This code has produced NO problems that I can feel (gas mileage is fine, engine isn't rough etc etc) - but people don't want to buy a car with an engine light, and I don't blame them.
I have seen various threads about the issue - but given what I have tried already, what would be my next step?
Is it just P0172 code, or are you getting the P0175 code too? Because if it's just the one code, then that means it's probably a bank specific issue. Which means it probably isn't your MAF sensor (which is the sensor you cleaned) or your throttle body, and could be something like: an O2 sensor, an injector, etc.
Well with it just throwing the generic "I'm running rich" code and zero symptoms I'm not really sure which direction to point you in. The fact that it's only reporting it in the one bank, and that you have no drive-ability issues makes me think it's an O2 sensor. Rock auto has them for relatively cheap, but it's still a crapshoot as to whether that's your problem. Hopefully someone else who has had this problem sees this thread and can shed some light on the subject
One guy says that disconnecting the battery for a long period of time will force a fuel trim relearn..... others have talked about using a GM scan tool to do it.
^+1. That's why a look at ST/LT fuel trims is valuable in diagnosing p0172/175 (rich) and p0171/174 (lean) codes. None of the 4 is a specific o2 sensor code.
I am going to have the fuel alcohol percentage checked today and see if it is being grossly mis-reported.
Also - now that both my O2 senors are working - they are wildly fluctuating. The guy said some fluctuation is normal, but they are both going way up and way down.
Are you monitoring the O2 sensor voltages or fuel trims? O2 voltages are supposed to constantly fluctuate - they constant go from reading lean to reading rich (very quickly) in order to keep the air/fuel ratio just right. So they'll read lean, computer will add fuel, then they'll read rich and computer will remove fuel. They do this constantly, very, very quickly, over and over and over in order to keep the air/fuel ratio "just right" (correct air/fuel ratio will vary depending on ethanol content).
From my 2012 tune, anything below 350mV will read lean and anything over 650mV will read reach. Looking at an old log file, my O2's usually fluctuate beween ~100mV and ~800mV. Constantly going up and down, alternating from ~100mV to ~800mV.
What are you seeing?
For fuel trims, generally speaking, you want your long-term fuel trims to be between -5 and +5. Short-term fuel trims will vary more, which is normal.
"(correct air/fuel ratio will vary depending on ethanol content)." - this may be it... After taking it to someone with a better read tool - we were able to see that the gas alcohol % being reported was 60%!!!!! And this is on standard gas - and after non-ethanol gas was added!
So I had to bring it to the dealer to get the gas relearn and PCM flash done. Now it is showing 1%....
Haven't put it through a drive cycle yet - but crossing my fingers hard!!!!
I noticed that the long term trim was at -7% (this was just going down the road - so not a lot of data for the computer) - the question is - at what percentage trim does it flag the P0172 code?
Drove the car - no light - passed Safety! Thank you for walking me through this very annoying process!
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