Howdy,

I have a P0138 Code on my 99 WJ 4.0. Says it's an O2 sensor...possibly a bad fuse. Both O2 sensor fuses work.

I have a non-California emissions Jeep. The best I can tell from actually seeing and diagrams is there are 4 sensors on the Jeep. Two are located underneath where the exhaust pipes come out. And two are sort of near the top of the engine.

The sensors underneath have a different connection than the ones on top.

So, how in the world do I tell which sensor is the bad one? Is there a different fault code for the sensors on top?

Thanks for the help!

Chris

 

Welcome to CF!

P0138 says "02 sensor input voltage too high." Check your 02 sensor wiring for a short from the heater to the input circuit. The heater is 12v and the input is 5v.

The PCM reads the 2 in the exhaust manifolds for fuel trim and the 2 downstream sensors for catalyst function. I would assume one or both of your upstream sensor's wires are shorted.