My daughter has an 05 cobalt with the 2.2L engine. The service engine light came on and my scanner would not read it (older Actron).....soooo she took the car to autozone and had them pull the code. It came back O2 sensor. We then replaced it with a direct fit Bosch sensor. The next day upon starting the car it set the code again. We tried a replacement sensor and now the same thing is happening. I probed the wiring harness on the vehicle end... (sensor unplugged) and found the ground like .2 ohms (should there be a direct ground?)
The grey wire on the Bosch sensor is suppose to be the ground, but it lines up exactly 180 deg off the car sensor ground. It will only plug in one way. Could it be a wrong part? I checked all the parts web sites and the part number seems correct. I am going in a circle. I need ideas, wiring diagrams or something to get me off this merry go round.
Thanks in advance!

 

Welcome to the forum...
can you post the code.. it may help in identifying possible causes....

 

Thanks
She doesn't remember they told her o2 sensor or circuit. The car is running so poorly that she won't drive it back to pull another code ...20miles of mountains. I assumed it was upstream since it ran poorly and was eating gas. Sorry i just can't buy a code reader right now. It seems like a wiring problem....just not sure. It is erractic, power one minute then very little.
The car has about 85K on it