I have an 05 cobalt and the engine light has been coming on randomly, usually for a few days then shuts off for a while before coming back on again.
I used an OBDII reader to pull code P0171, system too lean. I searched many threads online and have tried a few things but no luck.
The funny thing is the car isnt driving like its starving for fuel. What i have noticed is that i havent been getting great mileage over the last few years but i've noticed a HUGE drop in mileage lately. Like im getting 300km(186 miles) per tank.
Other than the terrible mileage and the car riding a little rough lately, there are no other symptoms other than the SES light. So i dont think the car's fuel/air mixture is lean at all.
this leads me to think that the upstream O2 sensor might be the culprit here ?
So here is my question. is it possible the o2 sensor is not reading the mixture properly so the car thinks its running lean when its really not. so its pushing more fuel to try to compensate for a problem that's not there, which would explain the terrible mileage?
i have also uploaded pics of the freeze frame info from the OBD2 reader. I am very new to this stuff and don't know how to read any of that info other than the MIL code.
Can someone here who knows how to read these things look at the pics and let me know if any of that info is out of the ordinary, or if any of that info can help narrow down the problem or prove or disprove my theory ?
Thanks so much guys !!!
Here are the pictures