Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Missing O2 sensor

I’m an experienced mechanic, and have never been stumped till now. My check engine light is on, and has been since I bought it. I checked the OBD code and it came up as P0138, down stream O2 sensor. Easy fix I thought. Problem is, there is no down stream sensor, not even a hole in the pipe where it should be. Upstream is there, but no down stream. My first thought is that someone monkeyed with the exhaust and clipped the wires where the sensor should plug in. Problem is, it appears to be factory issued exhaust, mopar stars and all. And I can not find even clipped wires for the plug in that should be there. Looks like it came from the factory with no down stream O2 sensor. I even checked to make sure it wasn’t a Mexican or Canadian model. It’s U.S. Any help would prevent an on coming mental breakdown. Thank you.

I would probably recommend changing the current O2 sensors, and see if that cures the issue.

I remember someone else on here before with a Chevy truck that had a hevy duty engine put in a light truck from the factory, that was being given a hard time by his state’s emissions testing facility. I think he had to get a letter from Chevy before the emissions facility believed that the truck came from the factory with the emissions package that it had.


What year is it? My 95 Dakota and 93 Caprice (OBD-I) only have one O2 Sensor before the cat. OBD-II was for 96 and later Dakotas.

Hello, It is a 2001, which means OBD 2. I’m wondering if someone didnt put a generation 1 exhaust on it. But it sure looks like the original factory exhaust to me. Thanks.

Was this issue ever resolved?

Check your ECM… Maybe someone swapped a different computer on this truck…and that computer is looking for its phantom O2…which it will not find and will complain endlessly about.