O2 sensor Problems

[jjk1224]

Late fall, I decided to fix the over due CEL issue related to the O2 sensor farthest to the back of my 96' 4.0 Explorer. I ordered the new sensor, and it was a tad short, so I spliced the sensor to the connector of my stock sensor. Two weeks ago, a snow storm hit us here in south east Michigan, leaving about a foot on the ground. During that week, my CEL came back on so I diagnosed the problem with my handheld OBDII reader and got the code "p0136". In my manual, the code reads that there was a circuit malfunction of the O2 sensor in bank 1 sensor 2 (the same sensor I replaced). I took the sensor off and upon inspection, I noticed some water had built up under the wrapping where the wires were connected, and the wires had corroded. I cut the wires again, and re-spliced, covered them back up extra tight so no more water could get in, and re connected it. About 20 min later, CEL came on again. Further diagnosis shows that the truck is reading a 141 and still the 136 code. I have no clue what I have done wrong, or what may have happened to the circuit, any help would be greatly appreciated.

 

[Cobraguy]

It's possible the sensor is doing it's job. The sole purpose of the downstream sensor is to monitor the converter. The PCM measures the difference in signals between the front and rear sensor to determine cat efficiency. Downstream O2 sensors rarely fail because cross count speed isn't critical. The only way to determine if the downstream sensor is operating is to use a scan tool capable of reading the datastreams.

That being said, I'm wondering why you had to cut the sensor leads. The proper sensor should have fit. Cutting and splicing the leads is a big no no on O2 sensors. The sensor creates such a small voltage (between zero and one volt) that any resistance at all can create erroneous signals to the ECM. I would replace that sensor with one that fits and see if that wasn't your problem.

 

[jjk1224]

Thanks, I replaced it with a new(right length) bosch sensor today, no CEL yet.

 

[Cobraguy]

Hope that fixes it for you!