That's a suspect voltage, and not an indictation of a good battery.

 

+1 After two days of charging I would expect 12.6-12.7 V

 

Hi and thank you bladerunner919/RJ237.

So are you really saying that a battery with 12.48v indicated at rest isn't capable of running the systems correctly on my XK8.

Will this really cause the car to lock itself in park and for all the dials in the instrument pack and centre console to rattle like crazy?

I also checked the vanity mirror visor wiring today. Can't see anything damaged, although the drivers side wires have some indents in them, as though something was squeezing them flat somehow.
I've also found a bit of foil which dropped through the hole when I pulled the visor clip out. It seems slightly sticky (tacky) on its rear. See attached picture.

Should that really be up there above the headliner?
It surely isn't part of the sun visor clip is it?

Any ideas what it's from?

 

​
Although I've only just sent my previous message, i've zoomed in on the pictures of the wires from the drivers side visor clip a bit more and I'm thinking there's a possibility of some breaks in the insulation that are too small to see with my bare eyes. The insulation at the areas that have been flattened is definitely not smooth and looks rough.

Could this be the cause of the issues, if it's been resting up on the chassis roof?

Happy to take advice from those much more knowledgeable on this topic than me.

 

Does this happen as soon as you turn the ignition on or only when cranking? If the systems are going crazy as soon as you connect the battery or turn the ignition on without cranking, its not a battery problem. 12.48v is plenty to run the electronics - the issue with a bad battery is when you crank the voltage can drop too low, it can still turn the starter, but not be enough for the electronics.

 

Hi dibbit,
Hope you're well.

The issue happens when I turn the key to position 1 and 2, where it seems the signal isn't there anymore for Ecu/bpm to allow starting now. Car acts like it's dead but I do all the spurious warning errors on the cluster, brake light permanently lit and 'Er' on the climate pack with rapid beep tones. I've been seeing intermittent issues recently over the few months, to the point where every has got worse and ultimately to the scenario where I'm now at.

Ih ad all grounds professionally checked back in January by an ndie Jag shop in Bury St Edmunds and thought we'd solved it, as a couple were found corroded. I'm thinking the BPM could have finally given up on me. I do have a correct spare part but want to check everything which is linked to there before I make the delve in to taking the glovebox out to investigate the BPM further.

Should the visor clips really have foil strips on the back of them?
The fact loose foil came out of where the clips go, with the fact there are wire contacts exposed in the clips inside, makes me think this might have been intermittently touching them and the exposed metal roof of the car.

 

I think you are wise to investigate further before swapping the BPM - you don't want to risk damaging the replacement if there is a fault on the wiring harness somewhere. As ever with these things, the wiring diagram for the car is comprehensive and you can do a lot of testing with just a multimeter.

If you do get to the point of taking the BPM out, you should open it up and look for damage/scorch marks on the circuit board as this would point to an external fault causing the damage.

 

Thanks for the reply dibbit,
Yes that's my approach for sure.

What do you think about the query in respect of the foil pieces which seem to have come off the back of the sun visor clip plastic mating pieces?
Do you think the fact these came loose may have caused a short?
Do they need to be there?

If something has shorted, given that the vanity lighting power lines are directly connected to the BPM it's possible the BPM has been affected and gradually got worse to the point where it's toast (although it may not be as crispy as the original poster Waldo's). I haven't had any fuses blowing either.

 

The BPM takes about 10 mins to remove from the car, so I'd whip it out and have a look inside. Disconnect the battery, remove the glovebox (two fixings at the bottom and a few screws across the top - remember that at the bottom there are two fastners on each side, but you only need to undo the outer ones, as the inner ones are only for alignment). Once that's out, the BPM is in front of you, bolted to the other side of a metal plate with three bolts. The actual wiring connector to the BPM has a bolt in the middle that you undo to release the connector. Job done.

 

Hi Bladerunner919,
Thanks! So no need to remove the airbag?
If it's that easy, I'll definitely check the BPM for damage regardless.

Also, as per my previous post, are you aware of the foil pieces on the back of the sun visor clips?
Do they have to be there?

The fact they've come loose and foil is clearly a conductor makes me think they've possibly intermittently shorted the vanity light wiring contacts to the roof of the car.

Thoughts?

 

Sorry,I don't know anything about the foil you found. I would start a separate thread and get opinions. What I would do is wrap those wires in good quality electrical tape to make sure that they are properly insulated.

 

The foil is there on all the one's I've worked on.Nothing to do with conductivity, just holds the plastic split together for easy install I guess?

 

Oh wow, so why did they use foil and not something like tape which wouldn't pass electricity.

 

It is tape.

Foil tape.

 

No, the airbag is above the glovebox, whereas the BPM is behind it.

 

Sure but foil conducts electricity right.

 

Don't apply any current to the foil and you will be OK. (or the steel body parts unless it is earth/ground)

 

Well i loosened the BPM cable connector and the the 3 bolts and it's loosened but how the heck do you get the module out. There's not much room to pull it forward and out as it catches up against the metal bracket. There's a bit of ducting for the heating system below where the BPM is. Does that have to come out?

I'm stumped and don't want to damage anything in there that I can't see.

 

Yes, remove the duct - there's one screw that holds it in place.