lazydan

Hello everyone,

I have an 05 cobalt ls 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?

The only other thing i can think of at this point is the MAF sensor. can i clean this with Brakleen?

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 if it points to anything like MAF or O2 sensor.

Thanks so much guys !!!

Here are the pictures

BozickA

iTrader: (2)

Your ltft is nuts being that high check for any air leaks after your maf sensor when the engine is cold spray some tb or brake cleaner around your intake or hoses and see if you can watch your fuel trims change drastically. If they do where your spraying is the air leak

BozickA

iTrader: (2)

Also you asked about o2 but I don't see any voltages for the sensor in there

lazydan

thanks for the replies. unfortunately this OBD2 reader is just a cheap little thing i bought and doesnt read o2 sensor voltage.

i have also checked for air leaks and could not find any. This leads me to believe whatever is adjusting long term fuel trim is causing problems or is faulty.

is it the upstream o2 sensor or the maf sensor that adjusts ltft ???

thanks

BozickA

iTrader: (2)

If you rev your engine what is the g/sec your maf is reading?

Normally a faulty o2 would have its own code say if you had a p0171 and a say a range performance code for the o2 then id say throw an o2 at it for both issues. But just a lean is unmetered air somewhere coming in or possibly injector issue hard to diagnose without a good scan tool that can change injector volumes if your MAF or a loose hose does not turn out to be the problem.

lazydan

thanks for replies, unfortunately my obd2 reader only lets me see info stored with the code. I cannot see any live info.

i guess to the shop i go.

thanks guys