Help, my XJ8 starting having this weird problem. When I turn off the engine, it keeps running. This first happened a couple of months ago.
Now the ignition lights just come on all by themselves and will drain the battery dead if not caught and battery neg diconnected.
I have tried everything I can think of.
Now the car will not crank unless something , not sure what, allows it to .
Pulled the ignition relay. which will only shut down engine.
Pulled the leads from the barrel which does not turn the ignition lights off. strange.
Have not seen any other posts like this.
Thanks Jim in Pa

 

I have a replacement ICM from another XJ8, but I don't know where it came from, I mean it's current location on my XJ8. Help here please. Jim

 

On my 1999 Super V8, I once had a problem that (with the key out and the car locked) the throttle body and the SC intercooler pump were energised by them selves, like when the ignition is "on". I cannot remember whether the instrument panel lights were also lit. I traced it to the alarm siren - the siren internal batteries were, due to some fault in the siren itself, energising a couple of relays that should only be energised with the ignition "on" and this caused the throttle body and the pump to run. I just disconnected the siren and the problem was solved.

You can check, when your instrument panel lights are on by themselves, whether your throttle body is also running (humming). If this is the case, then you may have a similar fault in the siren.

 

Yes, that is also occurring. I,m assuming you pulled the fuse for the siren? Or something else. Thanks Jim

 

No, I just found the siren (hidden a bit down low at the front left corner of the engine compartment) unplugged and removed it and threw it in the (recycle!) bin. No issues or warnings after that. The alarm still sounds the car's horn but I have no chirps when locking/unlocking the car, just the turn signals flashing (good enough).

 

Thanks, I did find the siren under the car and disconnected it along with the fuse for it. But no luck, lights still on and humming still happening. I'm thinking it might be The ECM. Jim

 

It may not be the ECM itself but it may be powered-up for some reason even with the ignition off. Se the diagram below - connect the battery and, with the ignition off, start pulling & reinserting the following relays one by one:

1. Ignition Positive Relay
2. EMS Control Relay

If any of these two relays clicks when pulled out and clicks again when pushed-in, that relay is, for some reason, energised even though the ignition is off. If they don't click but, when pulled out, cause the TB to stop humming, then that relay might be bad (sticking in "on" position).

If none of these two relays clicks when pulled out or pushed in, and if they don't stop the TB humming, do the same test with the Throttle Motor Power Relay.

Let us know your findings.

 

Thanks again. I did make progress. I had already pulled every relay and fuse, but none were the problem. And yes those relays you mentioned clicked off when pulled. After pulling the Siren connection to no help. I started pulling any and everything else I could find.. Now I had pulled the radio out to check and disconnect an Old Sirus power connection. after that I got the light to turn off and on. Getting closer! when I hit the glove box the lights when out. Mind blowing. got it to a point where I could push the light trigger and make the lights go off and on.
Next I disconnected the glove light altogether and pushed the wires back, this is after taking glove box out. Now I can start and turn off engine normally! Bizzaro!!

That was yesterday evening! Car sat overnight with battery connected for first time in almost a week. Not discharged! Yippee.. I need to test drive alot. The Problem is now I can't recreate in driveway.
I've been tinkering with cars for 44 years now. Never had a problem this weird! An old 94 ford explorer was close. The inertia switch connection came lose but still connected. would sometimes not start in driveway, but if you jumped up and down on rear bumper, that would allow it to start! LOL

 

Obviously, the ECM was energised by the relays that were energised by something even with the ignition "off". Did you check these relays again after disconnecting the glove box light and the Sirius power connection and found them not clicking anymore?

Keep experimenting and hopefully you will fix the issue without having to do a painstaking search through the wiring diagrams (like what I had to do to trace my issue to the siren).

Funny cars, these Jaguars - way too much electronics and things to go weird.

 

One month later update. Car ignition system seems to be working normally, However, I have been getting a P1647 error, saying that the Upstream Ho2 sensor is not heating correctly. Both have been replaced before this strange problem had started. So now I can't get the emissions test done and pass.
After checking everything I can, and a side distraction( 80ft paver path in back yard). Back to it now.
Testing the leads to the Ho2 heaters I got about 8.7 volts on each which I believe is the problem. this is on a 2000 xj8. My 98 xj8 had around 12 volts. Should be the same? yes?
Today I'm going to dive back into the glove box light lead to trace back what it was interacting with.
The two problems must be related.
My question is , does it seem likely the light lead, which is hot crossing with a wire that energized the ignition system also damaged the wire feeding the Ho2 heaters causing the voltage to drop. this must have been a backwards feed energizing the ignition system. Thanks Jim

 

Maybe (as in: I don't know but I like your reasoning).

With luck the Electrical Guide for your car goes into detail, showing such as splices, ground locations etc as well as fuses, relays, wire colours and so on.

You might be able to remove some fuses for things you don't need when troubleshooting to see what is then still powered or not. Take notes & photos!

 

Just got done putting dash back together. Pulled apart the lead with the glove box light and 3 other wires. No sign of any breaks or anything else. the 3 other wires, 2 black and 1 orange. the 3 black went back towards the gauges and tthe orange and red when the other, followed the orange down to an connector which looked like a dead end. taped to that leg of harness. the red went to the glove box light.
AT least everything seems to be working right now including glove box light , except for the P1647 code.

Then a new test idea, unplug the Bank 2 Ho2 sensor and hook up the old other side one and ground it out. reset the pre P1647 code and start engine. On a test before the pre P1647 code came right on. Now after warming engine Bingo the code doesn't reappear, and yes the Ho2 sensor got hot.
Well if it walks and quacks like duck. Bad replacement Ho2 sensor, maybe caused by the ignition being on all night twice running down the battery.twice before staying on like in other posts!
Tomorrow swap out the Bank 2 sensor with a new one! Royal PITA
Thanks for reading and replying, It really helps!