bbigg

I have been chasing electrical problems on my 96 XJ for a few years now. I have O2 sensor issued on the downstream side with the heater circuit CEL intermittently. I started chasing grounds. I noticed that all my grounds were reading about 3 ohms or more fromthe neg batter terminal to the various gnds on the car. I disconnected the battery terminals and saw the same thing. There should be no connection between the pos and neg battery cables. Started isolating then by pulling fuses inthe PDC until it went to an open line. I have my meter on the pos and neg battery cables with battery disconnected for the test. The 20 Amp fuse in the PDC was pulled and I got and open line. That fuse controls the fuse panel in the car. I started pulling fuses inside the car until I got an open line and no luck. Something must be shorted between the PDC and the inside fuse panel I am assuming. Any thoughts. No fuses blown. Car runs. I do have flickering interior lights at idle.

nujeepguy

ohm

bbigg

With the battery disconnected, all my grounds ring to the neg battery terminal correctly (about .003 ohms). When the battery is connected, my resistance goes up to about 8 ohms when I put one lead on the ground point on the frame or engine block and the other on the neg battery terminal. I traced it to the underhood lamp. When I remove the bulb the readings go normal. There are bulbs everywhere on the car. Why does this one bulb cause this? This small short is causing all sorts of small anomalies. Have you ever heard of this before?

freegdr

Hood open ?

bbigg

Yes but there are many lights on the vehicle. I don't understand why this one messes with the ground readings.

freegdr

Might be the unit it self or bulb are going bad.

fb97xj1

I dont know how the 96 is wired, but the FSM for my 97 shows the hood lamp is on the same power distribution circuit as the rest of the courtesy lights and drivers door lock/window switch, via the JB. The hood lamp shares a ground with a bunch of stuff as well (VSS, ABS, wiper motors, TCM, NSS, etc.). Your 96 may be different in places. My point is that one component can affect a bunch of stuff being on the same circuit. The XJ is a mess when it comes to wiring. Over engineered.

Disconnect the hood light. Problem solved. If thats not an option, take it apart and clean it. Might be dirty, or the bullet went bad. Check the plug and wiring, too.

bbigg

Thx will do. Ultimately I'm trying to solve my p0138 O2 sensor issue to pass emissions. I thought maybe that anomaly would contribute to all the chassis grounds being shorted. I pulled the bulb and the short went away. I'll drive cycle the jeep to see if the emissions readiness clears up. It usually takes a day or so to drive cycle it to meet the readiness state. It fails at that point. I also checked my source voltage at the O2 sensor and grounds. The sensor is just about new. I replaced them both recently. The heater circuit in the sensor checks out with the ohm meter. We'll see soon enough. thanks again

nujeepguy

if

CurrySoSpicy

Yes ohm measuring is a circuit off test. This is because your digital multimeter doesn't just magically know what the resistance is when you place your pokey bits on things.

it sources a known voltage over the closed circuit and monitors the voltage drop. Knowing this, it calculates the resistance.

So basically, the meter can't function on ohms if your sourcing two voltages on the circuit (multimeter and car battery).

bbigg

I checked the main lug on the PDC already. I did pull all the fuses once and nothing stood out. I'll check again. Thanks

CurrySoSpicy

Well here is the elephant in the living room. Have you investigate the O2 sensors circuit wiring?

bbigg

I looked at the sensor itself. Tested the heater wires. I tested the voltage from the ASD relay. The sensors are fairly new. I took the skin off the rear O2 sensor back to the next tranny sensor. Nothing burned or broken. The only thing I can think that is causing the p0138 is that the ASD voltage is making it on the sensor signal to the ECM from the sensor. That would mean something wore through or burned. I would have to pull back a lot of skin covering the harnesses to find it.

bbigg

Well folks. After removing and reinstalling connectors on the downstream O2 sensor and cleaning the throttle body well. My Jeep passed emissions. I used my code reader to verify the readiness before going to inspection. I also found out my high idle was due to the cruise cable getting hung up after warmup under the hood. I verified this by disconnecting at the throttle body. Thanks everyone for your posts.

CurrySoSpicy

cool dude. Thanks for the update.