I've had the check engine light on in my 1992 240 sedan since I bought the car at the end of June. I checked the code under the hood, and the only one reported was 212 (O2 sensor). I replaced the O2 sensor last week, and reset the codes. After about 5 minutes of driving, the CEL came back on. The code was 212 again.

I've cleared codes a few times only to have it come back. I've checked the wiring connections, all are good. I'm not sure what else to do, any suggestions?

 

Just a thought - I have heard of people having issues when they replaced the O2 sensor with a generic one, which is much cheaper, instead of the specific one called for. Which kind did you use?

 

its fixed! I read a lot of different posts with check engine light issues, and a lot of them said to disconnect the battery, so I decided to give that a try. I also replaced the fuse for the O2 sensor. I'm not sure which one fixed the problem, but I'm happy its fixed.

Oh, and I used a bosch sensor.

 

Bosch is good.

 

Just saw this. I'd be inclined to say the fuse did not have a good connection. If a code keeps returning, it's usually time to drag out the multimeter and check voltage at the sensor AND at the ecu. Assuming voltage is appropriate at the sensor but not at the ecu, work backwards. It's great that you resolved the issue so easily! Disconnecting the battery will erase the codes exactly the same as resetting the OBD module. Alone, it will not keep a code from returning if the OBD module will erase it initially.

 

I've heard that not only in these cars but others that a 02 sensor code 8 out of 10 times can be a vacuum hole that has a small leak. It throws off your oxygen levels. Hope it helps