beyondkreativ

I have a 1997 Cherokee SE 4.0, 4WD. Does anyone know where I can find a "new" engine wiring harness? Or at least the part of the harness that goes from the ECM to the coolant temp sensor (ECT) and upstream O2 sensor. I can't find a diagram for that harness either...

CCKen

I don't think you'll find a 'new' harness. You'll have to go to a bone yard and remove what you need. Keep in mind that those wires you are concerned with are spliced into other sensor wires serving the same function as the ECT and O2S, and would require cutting and splicing into your Heep's harness.


Why do you need this harness anyway?

beyondkreativ

I have a short somewhere in the harness from the ECT to the ECM. Read the computer and it is showing "coolant temperature sensor low input". Replaced the cluster, ECT, wire connector to the ECT, and the O2 sensors. A few mechanics looked at it and couldn't find anything wrong with it... besides the temp gauge randomly losing signal from the ECT, or ECM... whichever is the case.

CCKen

What is the exact code number you see?


Could be the ECT signal wire (Tan/Black tracer) shorted/partially shorted to ground.


Inspect the wire harness loom where it exits the fuel injector wiring manifold and makes a turn to join the larger loom against the firewall. See if the end of the fuel rail has rubbed through the loom and into the wiring within.


Similar to what you see in this photo:

beyondkreativ

The code is P0117 (coolant temperature sensor low input).

While I am driving, the temp gauge reads about 210. Randomly, the gauge will jump up to 240ish and drop down to lowest reading (100)... then it will rise back to about 210. It has been a completely random problem. Some days it will not do it at all. Some days it will do it the moment I start the engine after sitting for hours.

I have had it checked out by a few different mechanics and have spent over $400 in effort to figure it out. Everything is new except the PCM and the wiring. Though I did replace the ECT connector.

beyondkreativ

I just checked all the wiring and did not find any cracks or damaged wiring from the ECT to where the wires go into the harness at the firewall. However, I did find that the ground strap from the engine to the firewall was broken. Could this have anything to do with my problem?

CCKen

Not likely but it should be fixed.


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Here's possibilities for P0117:


ECT Sensor Signal Shorted to Ground
ECT Sensor Signal Shorted to Sensor Ground Circuit
PCM


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Here's the wiring diagram for the ECT:





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Try this:


Operate the engine until a temp reading is registered on your temp gauge.


Have a helper sit in the Jeep to keep an eye on the temp gauge.


Turn the ignition switch to RUN (don't start the engine). Helper should see the temp reading.


You'll be wiggling wiring harnesses so have the helper yell out if the temp reading changes.


Wiggle the wiring harnesses, starting at the ECT wiring where it enters the fuel injector wiring manifold, then out of the manifold, then the smaller of the two looms against the firewall down to the PCM. The ECT wiring enters the PCM at the Black PCM connector (the other two connectors are Grey and White). You may have to remove the air filter box to get a wiggle on the wiring entering the PCM connector.


If the temp reading changes when wiggling the harness, that's where the fault is.


If there is no response when wiggling the harness, start the engine and repeat the process.

beyondkreativ

Thanks for the diagram. I will have some time to look at it tomorrow and maybe narrow something down.

Last night it occurred to me to try the wiggle method. No change in temp reading. Though, I did find a wire coming from a little box (with only two wires) mounted on the passenger side firewall going to the negative post on the battery was broken, so I grounded it. Also fixed the ground strap from the engine to the firewall and have had NO symptoms since doing that. Today I drove it 30 miles to and from work (mostly Highway) and some in town driving and the temp gauge was steady at @210. Usually, the temp gauge will start jumping up and bottoming back out after only 15 minutes. I 'tried' to make it show a symptom today and got nothing...

The randomness of this situation has been very annoying... and expensive so far. I really hope to find and fix this ASAP. I worry that it is a sign of something else I need to fix.

CCKen

Here's what Jeepers do....If it doesn't affect the performance of the engine or trans...turn a blind eye to it. LOL