greasefairy

Hey yall, after replacing my TCM and MAP sensor my '97 Cherokee 4.0 started throwing P0135 for the heater circuit in the upstream O2 sensor. It's been accelerating slowly and bogging down while driving since the new TCM went in.

I threw a new sensor on without testing the existing sensor first (replacement was a walker because I couldn't find NTK or even Bosch anywhere locally), and the problem persisted even after wiping the codes and putting it through a couple drive cycles. Popped the little 15A fuse under the hood four times before deciding to test the new and old sensors - the old sensor was still reading fine so I threw it back on and was still having the same issues (bogging, poor acceleration, fuse blowing).

I've traced the wires all the way up through the engine bay and the only problem I found so far was by ground G101 where the ground wires for both sensors had the casing chewed off by friction. the wires inside looked fine otherwise, so I taped them up hoping that was the issue, but it doesn't seem to be. The jeep is running fine and not blowing that fuse with the O2 sensor unplugged, so at this point I'm feeling confident that it's not another issue showing up as code P0135.

Could it be that the wiring harness that leads up to the PCM is shorted somewhere? (I've found no other indications that the PCM itself is the problem). Could it be that I just need to track down an NTK O2 sensor? Should I go back and crimp those chewed up wires by the ground even though the wires themselves look okay? Could the connector that the sensor plugs into be shot? Did I somehow knock or blow something related to the sensor while I was replacing the MAP or the TCM?

I've read what little there is in my Haynes manual and read every forum post I could find on multiple sites about similar issues. New to using a multimeter - any tips on tracking down this short or info from the FSM would be much appreciated. I'm about ready to rip my hair out. thanks for your patience y'all, i know that's a lot of words

bluejeep2001

What was the colors of the wires that were damaged

greasefairy

they were the ground wires for both of the o2 sensors! the jackets were scraped off but the wires did look normal otherwise.

bluejeep2001

Thats the point, if you don't know the colors...then you don't know what the wires were. Shorted ground wires to each other or to metal grounds don't blow fuses. An open ground will disable the heater

awg

just use a multimeter to test the harness

while it would be best to check circuit diagram, wire color etc

if strictly checking only for shorts, test for resistance between each wire, it should not be near 0 ohms, wiggle the harness while testing

with harness connected, probably only one wire should be grounded

check circuit diagram is best

a short can fry the pcm