Have 99 XJ8 . Every now and then the car goes completely dead. No power to anything . The battery was checked and its good. The way I get it started again is to disconected both battery terminals. Then it starts. Also when this happens , I checked the large 12 volt power wire under hood on the right side by hood latch. It shows no power. But when I reset car by un hooking both battery leads and then check it, there is 12 volts of power and the car starts. So is there a relay somewhere on car that is making this happen or ECM problem or grounding problem or ???? Any help greatly appreciated spuds1956 donmck1950@aol.com

 

It seems that XK & XJ seem to have a problem with clean electrical connections. I am attaching a general oneline of the main electrical feed to the starter and engine control fise box under the hood. It appears you did a little checking and found no voltage until you began moving the battery leads and that leads me to believe your problem is more locally located near the battery. This could be the terminals and or the high power protection module. If you are not getting power to the front of the car at the power distribution points at the fuse/relay boxes you need to work your way back to the battery. I hope this helps!

Note: Prior to cleaning your connections disconnect the battery!

 

Were is high power protection module located on my 99 XJ8 ? Really appreicated the help!!

 

In the trunk next to the battery.

 

Spuds1956 I am having the same condition you describe, what did you find to be the cause?

In my case I can wiggle the battery cables (they have been cleaned and no they are not loose) and it's fixed until the next time. I'm thinking its something in High Voltage Protection Module or a broken positive post in the battery, but wondering what you found.

 

You might be surprised at what you find if you take off the negative battery terminal at its grounding stud. Mine appeared to be perfectly secure, and did not wiggle at all easily, but it was slightly cocked on the stud and did not always make contact as it should. When I took it off you could see evidence of arcing.

It only takes a minute or two to take off and check. You'll also want to see if the connector itself or the stud appears to have any corrosion. The stud itself often turns out to be covered in paint near the base and the only contact that's made is if it's worn through and making contact with the flat surface of the connector. If the paint is particularly thick the only contact might be the inner drilled edge of the connector and the stud. Even the slightest corrosion on either the stud or that inner edge can create significant resistance.

Another member of these forums made a suggestion that I also make: Manually clean off the connector and the stud and coat each with electrically conductive grease, which effectively prevents corrosion "perpetually" and increases your conductivity.

See this thread, which should also help you as far as tracing out potential failure points in the electrical supply system (with a big thanks to user plums).

Brian, who despises electrical gremlins with a passion

 

Today I had the random no power condition again but this time I had a volt meter handy. I found I had 12+ volts at the battery but only 2.5 volts at the incoming connection at the high voltage protection module. Moving the positive cable at the battery slightly increased the voltage.

The problem was a weak connection between the battery terminal clamp and the cable although it looked good and there was no corrosion. A new cable would have been the fix but I have a large cable crimper so recrimped the connection which corrected the problem. The interior lights even seem brighter.

It seems odd that you could move the cable slightly and start the car but would get intermittent no power conditions with nothing but the radio on. Feels good to fix something on the Jag without it costing hundreds of dollars.

 

Good find!

 

I think i have this issue, moved the car on the drive and then the car cut out and there was no electric power in the car.
If i check the battery it says 2volts, if i disconnect the battery it slowly goes back up to 12+v. everytime i connect positive the voltage drops to 2v??
Any ideas?

 

It is likely a bad cell in the battery, or just a dead battery. There is always a slight draw on the battery, and that appears to be enough to totally discharge it. You could try charging it overnight while disconnected and see if it recovers. Do you have removable caps on the cells, and if so have you checked to see if they some are dry?

But I think it's time for a new one.

 

Its only 12months old??
Will try another to check

 

#1 check your grounds!!! If your earth lead is loose then it can cause all kinds of funky electrical issues. Anytime I have any kind of issue with battery or electric I check connections and grounds. Good luck!

 

Check the electrical link in my signature. It has all the info on the common issues and testing info.

 

Hi everyone. I hope you don’t mind me resurrecting this thread. Dad’s having similar issues at the moment but not quite the same.

He maintains it with little regard to cost which can make him a bit of a target for the mechanic, despite his loyalty! Before I take it anywhere, I want to see if I can identify the fault or at least rule things out.

The car isn’t being driven much due to his health, but is being serviced / MOTd to schedule. I take it for an occasional run to keep it. Last serviced April 2022 (10 months ago).

There have been several occasions when he’s gone to start the car for the first time in a couple of weeks. The interior lights have worked, central locking, all the pre-ignition warning lights when he turns the key, but he just gets one click instead of the starter motor. He can turn the key again and get another click.

He has been charging the battery for a few hours with a good quality Halfords charger, but (brace yourselves!) has been charging it in situ still connected. After a few hours he’s tried again and it’s started perfectly well.

He recently went to start it after about 16 days and it was completely dead. No interior lights and nothing from the instrument cluster when he turned the key. Only the remote central locking worked. 16 days prior to that I’d driven it for a couple of hundred miles.

He doesn’t think the battery is very old but I can’t trust his memory these days.

So, I’m my convoluted way, I’m wondering;

1). Would it be useful to buy a battery meter and will this reliably tell me how healthy the battery is and how well the alternator is working?
2). Will it tell me if something is draining the battery? If that’s expressed as a number / volatage, what would you expect the background drain to be on that car?
3). Can anyone recommend a good value battery tester? There are some on Amazon less than £20 and but I don’t know if they’re useful in a car like this.
4). The car has a high spec which includes a car phone. That’s not connected (it’s still inside the front armrest) but something to do with it is next to the battery. I wondered if that could be draining it?
5). Could charging it in situ have done something to cause it to completely drain / damaged something, that caused it to go totally flat?
6). Is there somewhere in this forum where Jaguar specialists are recommended by members? I wondered if that was forbidden. Depending on my findings, I might need one, in the Southport / Manchester / or broader NW England area.

Thanks for reading this far!