O2 Sensor Shorting Issues

[Duneger]

So, I bought this 2004 Jeep Liberty with a rod knock from a drunk in North Dakota. Did an engine swap and ****** rebuild.

Got everything back together and I've got intermittent voltage short in both down stream O2 sensors. Codes p0137 and p0157. When looking at my obdII reader, it randomly drops to 0.0V and lasts no longer than a minute or so.

Right as I was going to start troubleshooting my multimeter killed itself. I'm waiting for a new one in the mail. I also bought a short tracker to help in finding out where the short is.

Anyone have a good guess as to where I could look for a short in the harness? The ground G103 looks solid and I tested it before my multimeter committed suicide and it was golden.

 

[Duneger]

I went for a long drive to confirm something. They both don't cut out at the same time. B1S2 generally cuts out more than B2S2, but usually not at the same time.

 

[Billwill]

I have all the wiring diagrams for the KJ with the exception of the 2004 model so cannot give you any detailed advice as the wire colors tend to be different between the various years.

If you cannot physically see a wire chaffing to ground there could be a problem where the wires enter a large harness that you are unable to get access to....two wires within the harness could be chafing against each other giving you a partial short to chassis via the other wires path to ground somewhere along its way about the engine bay.

You would need to completely isolate the suspect wiring by disconnecting all ends including splices so that the wiring hangs in mid-air. If there is still a short or partial short to chassis/engine then you need to cut off all the ends of that wire...whatever color it happens to be. Then replace that wiring...including splices..with new wiring...taking the shortest point-to-point route.

Been there done that after a front end collision damaged the harness.:emotions34:

 

[Duneger]

Yeah, in a last ditch effort I was going to just rewire from the sensor to the pcm. Might just be the quickest solution though. Only problem is I don’t have a dependable diagram for the pcm O2 downstream sensor location. I have it for the 2005 KJ, not sure that’s correct. My Alldata diagrams are lacking in the pcm department.

So, just need to cut out the old signal wire and splice in a new one from the o2 harness to pcm? Do the same for ground?

 

[Billwill]

Yeah the only 2004 KJ manuals to be had need to be paid for looks like. and

The ASD relay and the O2 heater relay should be swapped over with identical ones...these apply +12 volts to the O2 sensors and may have an intermittent fault.

It seems to me that pin 4 of the connectors you should be able on the harness side to measure to ground to check for any short. These wires from 1/2 sensor and 2/2 sensor pin 4 may have the same colors. So at the PCM, probably connector C1, these two wires appear somewhere.

Measure these two wires at the PCM connector for continuity back to the sensors and for no leak to ground when the sensor is disconnected and the PCM connector C1 is unplugged. These two wires could be cut at both ends, sensor and PCM, and new wires used to replace them...do not get them crossed over if they are the same color!

Pin 1 on the connector should have +12 volts on it when everything is powered up, pin 2 should go to chassis ground, pin3 on the connectors pick up ground switched by the PCM when everything is powered up...each sensor picks up ground from the PCM at different pins on the PCM. Likewise these wires from pin 3 on each sensor need to be checked for short to ground or open circuit.

A good Service Manual to use is the 2006 KJ Service Manual although the wire colors will be different and where they plug into the PCM will be different. The reason it is a good Manual to use is that in the Index right at the end is a DTC Index where you can look up your CEL codes....go to the relevant page as directed and follow the general steps on how to diagnose the problem. It calls for the special tool that the Dealers get to use but the advice given where it tells you to use a Multi meter is still valid.

Jeep KJ Manuals: Index of /manuals/Jeep/KJ