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Hey everyone,

A friend of mine bought a 2006 Chevy Cobalt SS (n/a) a couple of days ago. She took it for a test drive, at which point the check engine light went on. Dealership tells her not to worry, they will have it fixed and ready for her to pickup the next day. When she got home from the used car dealership, a check engine light came on again. Used my scanner and found out its a p1174, fuel trim cylinder balance malfunction. We took it back to the used dealership, and talking to the mechanic we determined it was likely a vacuum leak or faulty O2 sensor.

They claim to fix it, fast forward a few days, and the light comes back on. Understandably, we are getting quite frustrated with having to go back and forth to get this issue sorted out, so here is my question:

What would be the best way to go about fixing this? I'm pretty good with fixing cars but she lives an hour away and obviously I dont want to fix the dealership's screw ups, so I would like to know the best way to explain to their mechanic that resetting the system or erasing the code clearly is not the way to fix it (as this is our third time having them "fix" it).

Thanks,
Mike
 

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You might have a dirty injector, try some gas additive! Or a non OEM HO2 sensor.

From service manual...

DTC P1174: Fuel Trim Cylinder Balance
Circuit/System Description
The Fuel Trim Cylinder Balance diagnostic detects a rich or a lean cylinder-to-cylinder air/fuel ratio imbalance. The diagnostic monitors the pre-catalyst heated oxygen sensor (HO2S) signal's frequency and amplitude characteristics by calculating an accumulated voltage over a predetermined sample period. An imbalance is indicated when multiple samples of the accumulated voltage are consistently higher than the desired value.

Diagnostic Aids
• The Fuel Trim Cylinder Balance diagnostic is very sensitive to HO2S design. A non-OE sensor or an incorrect part number may set a false DTC.

• Monitoring the misfire current counters, or misfire graph, may help to isolate the cylinder that is causing the condition.
 
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