THare22

My check engine light came on so I ran an ODB II sensor and got code P0138, which was a 1 2 oxygen sensor shorted to voltage. It outlines possible fixes as the HO2S being damaged or failed and or the PCM has failed. Essentially the O2 sensor from my interpretation. Just curious if anyone has had this problem and has any direction. Want to avoid paying someone for something I can do myself.
Thanks

DFlintstone

Oh, I'm not that familiar with yours. 4 wires? a ground, a 5v sensor feed, the sensor signal to the PCM, then a 12 volt wire for the heater. (it has a little heater!, I believe).

I think if your wires to ether the front, or rear get bogered, and that 12v heater wire touches the others it will register as seeing high voltage. Just something to check, I guess the wires running to the rear can get some abuse, and they all end up near the hot pipe...

THare22

Honestly know very little about it , where are the wires I should check ? And are they touching the exhaust?

DFlintstone

Well that might be the question. the 02 sensors are after your exhaust leaves the engine, then at least one more back after the cat. I'd bet you could google something....

OutBurst

I had a couple codes going: P0138 and one for the cat not working. Apparently my '96 Cherokee never had the Cat/ECM recall and the cat was really, really bad. I bought a couple Oxygen sensors and made an appointment at my local Jeep dealership to have the recall performed. They ordered a new cat, installed it, updated the ECM, installed the new Oxygen sensors I provided and I was off.

P0138 did not appear immediately but it did after 10 miles of driving. I went back to the dealership and since it wasn't directly related to the cat, I wasn't going to push for them to figure it out on their dime.

I did a lot of research: I checked the fuse (it was good), checked the ground (it was good), I even cleaned up all the battery terminals and all seemed well. I checked both the oxygen sensors and they were connected and in tight with no leaks. I really had no freaking idea. At least until I checked beyond the oxygen sensor connections. It appeared that just beyond the rear (downstream, just after the cat, before the muffler) oxygen sensor male connector (that comes from the vehicle), one of the wires was completely frayed from the connector - thus unable to send information to the ECM. I cut the connector off the oxygen sensor and the connector from the vehicle and spliced the wires together - taking time to make sure the wires matched up as the connector would have it - just take the time and write everything down.

VOILA! BINGO! THAT'S THE WHOLE ENCHILADA! That was my problem - a stupid frayed going into the male connector on the downstream oxygen sensor. I started the Cherokee up, cleared the code, and drove 40 miles for about an hour and a half. No code! I think I got it, Johnny!