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98 XJ wont turn off engine with ignition key (SOLVED)


NAXJA Forum User
I don't post here much, but this was a head scratcher of a fix that I want to share.

A few days ago, my son came home from school with his 98 XJ Classic and sat in the driveway, idling for a few minutes. in a few moments, I heard the sound of the starter grind and then about 3 minutes later, he walks over to me and says "Dad, the Jeep wont turn off with the key!"

So, I sit in the drivers seat, and sure enough, the key is off, and I even take the key out but the engine is running and all of the instrumentation is working. I work the key back and forth a few times, with foot on brake, without foot on brake, tilting the column violently, wiggling the gear shifter, pound on top of the dash...all of the typical fixes :), but nothing is making the XJ turn off.

So I pop the hood and pull the shutdown relay and everything shuts down, however, I notice I still have power to the cluster, particularly the odometer is still showing total mileage, which is very obvious to see when the key is off. I put the ASD relay back in and start the XJ up, and same thing, it wont shut off with the key in the off position. Its not dieseling, it is running perfectly...its just not getting the command to turn off the engine.

Thinking this is a bad ignition switch, I put in a new replacement, but still have the same problem...sigh.

So I start pulling fuses one by one in the PDC and get to fuse 9 in the PDC, a big format 20A fuse that powers the AC relay. Fuse 9 also powers fuse 27 in the PDC. I put fuse 9 back in and pull fuse 27 to isolate that circuit and still have the problem, so the problem is isolated to the circuit powered by fuse 9 in the PDC. Referring to the wiring diagrams, fuse 9 in the PDC controls the AC clutch relay. Since all it does is power the AC compressor clutch relay, I swapped a spare relay into the PDC and the problem is solved!

I have no idea how a bad AC compressor relay can backfeed power into the computer system to keep things powered, but it did. In hindsight, a few months earlier, I noticed the AC was not working, but didn't give it much thought as there are four perfectly good working windows on the XJ that give plenty cooling at 70 MPH. That was a precursor to this problem as changing the relay not only fixed the no shutoff situation, but also restored the AC to working condition.

Passing this fix along to those chasing a "wont turn off the engine with the key" situation with their late model XJ. This was a head scratcher and a totally unexpected fix. I was expecting to have to dissect the steering column looking for shorts when the ignition switch didn't fix the problem, but pulling fuses one by one to isolate where the problem was occurring was key. My troubleshooting lead me to an unexpected place and an unexpected fix.

Paying it forward.:cheers: