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post #1 of 4 (permalink) Old 01-24-2013, 07:20 PM Thread Starter
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Please Help Reading Freeze Frame Info

Hello everyone,

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



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post #2 of 4 (permalink) Old 01-24-2013, 11:35 PM
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Looks like your Cobalt needs a basic tune-up. MAF and tb clean, plugs,air filter and cat check.

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post #3 of 4 (permalink) Old 01-25-2013, 11:44 AM
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When my rear o2 went bad I lost 7mpg because the car thought it was running lean and dumped the fuel to her. No reason I can see why the front o2 couldnt do this aswell

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post #4 of 4 (permalink) Old 01-25-2013, 03:23 PM Thread Starter
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Quote:
Originally Posted by Coby7 View Post
Looks like your Cobalt needs a basic tune-up. MAF and tb clean, plugs,air filter and cat check.
thanks,

but I change my air filters regularly, and i did the plugs last year, cat has nothing to do with this code and is not an issue.

as for the MAF, that is why i posted the pics of freeze frame data, if there was an issue there im sure it could be determined from the info i posted. However, i do not believe that is the problem.

Im wondering if anything is concerning in those numbers, for example the Long term fuel trim is almost at 20%. I do not believe it should be that high ?

possible causes? o2 sensor is one right?

thanks


Quote:
Originally Posted by money_man View Post
When my rear o2 went bad I lost 7mpg because the car thought it was running lean and dumped the fuel to her. No reason I can see why the front o2 couldnt do this aswell
thanks for the info, still looking for someone to look over the info in the pics to let me know if anything is out of place. Ie. LTFT, should it be that high?

thanks
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