My car is a 2008 Chevy Cobalt 2.4l with 206k miles. I've been having issues with my oxygen sensor lately. I checked on it some months ago and noticed the o2 plug had come loose and was resting on the heat shield. The sensor side looked badly burned but not the harness side of the plug. I got a new oem o2 sensor and installed it, cleared the codes and drove around for a bit. After some time the check engine light came on and gave me these codes:

p0030
p0053
p0131
p0134
p0135

I checked the resistance on the new sensor and got about 6 ohms across the 2 heater wires. I'm no mechanic so I'm not sure if that's good or bad.
I'm thinking the harness side of the plug is messed up from getting too hot and was going to cut the connectors off both sides and connect the wires directly.

Thoughts?

 

I'd start by checking the wire to the ECU from the plug, remove the loom and inspect for breaks, nicks, and burned spots.

If that all checks out ok, I'd lean towards a bad O2 sensor, which can happen but isn't likely on new ones unless you put never seize over the senor.

 

Inspect the pins inside the connector on the car harness side. Not on my Cobalt, but over the years working on cars I've seen a few where moisture gets passed the seal of the plug and corroded the pins.

 

I appreciate the responses. The wires all look fine, they are a little oily near the computer but no breaks or burns or anything else of note following the wires. I put the o2 sensor on out of the box, and didn't apply anything to the sensor.
I checked the pins on the female connector and didn't notice any damage or corrosion.

Not sure if it helps but the car runs completely fine with the plugs disconnected, but fairly rough when connected. Especially when idle, I even had the engine die at a stoplight.
My little OBDII computer says 0v from sensor 1 (The one that's been causing me issues) when plugged in. Fumes are a lot stronger when it's plugged in too.

 

Sounds like a bad sensor then. It might have a warranty

 

I replaced the O2 sensor and same issue. I took the lower connection off the pcm and found it saturated in oil. I cleaned it all out with contact cleaner but still same issue. I noticed the voltage is now all over the place for the sensor. Anywhere from 0v to .5v and it runs pretty rough. I'm only getting codes p0030, and p0135 now. I tested the sensor and am getting a resistance across the heating wires. I'm not sure what else to test. So you think it's a bad pcm?