Hi everyone.
Need some help with my 1998 XJ8
The alarm has started going off during the night and each time it happens I find that the Trunk/Boot has opened by itself. Normally I have no boot open alarms. Only happens maybe once a week but is annoying the nieghbours.
My local Garage has suggested voltage drop may be triggering the alarm.
My question is, If the battery voltage drops does the latch automatically release, ( to give access to the battery maybe ), or am I looking at the wrong cause. The battery is resting at around 12.2v.
Don`t want to go to the expense of a new battery if the latch itself is the culprit.

 

Most unusual. No, as many members have found to their cost, the boot doesn't open when the battery gets flat.
I'd suggest getting your battery load tested - battery shops will do that for free.
Low batteries can cause all sorts of surprises but opening the boot isn't normally one of them.
You're not near any high power transmitters are you?
I had fun with the Royal Radar Establishment causing locks to cycle madly.

 

No, no transmitters to my knowledge. The car is parked where it always has been for the last 3 years without problem. I first tried re-setting the alarm with the key fob from my bedroom window, but of course, 5 or 10 minutes later it re sounded. I now find that if I unlock with the keyfob, re-close the boot/trunk and then re-set the alarm, it`s OK again for another week or 10 days. Poltergiests maybe.

 

Beats me. All I can suggest is the battery check.

 

Maybe you could try re-programming your key fob. I read that the "newer" Jags had rolling codes like garage door openers, but the older ones did not.

 

Thanks for your suggestions. Think I will try the battery check first. It is the original battery so at 15 years old it could do with changing.
How exactly does the boot/Trunk lock function. Is it a mechanical lock moved by a motor with an In position micro switch and if so, does the motor open it or close it ?

 

Would it be worth trying a Hard Reset? Maybe your Security Module's Memory is in need of a Spring Cleaning.

Oh, and an 15 year old battery should be changed for many reasons... Also, put into Guinness.

 

Hi and thanks for all the help. Much appreciated.
OK, so my alarm sounded again at 3am this morning and again the boot/trunk lid was open.
Had time to have a good look this morning and noticed that the trunk lights were also not working, number plate and tail lights OK. Battery was now reading 12v exactly so I recon its about to give up and I will replace it tommorrow.
However, following your advise I performed a hard reset and immediately the trunk lights now work.
Have I solved my alarm problem. Watch this space.

 

Not without a battery swap. I've not heard of this happening and it is most undesirable that it does but low battery volts cause most bizarre random module corruption and I suspect that's what you've got.
ps make sure you've got the radio codes otherwise you'll need to jumper a battery whilst swapping.
Oh but you did a hard reset so must have the codes.

 

Yes, Thanks Steve.
Code went in OK so the traumer of a Hard Reset and a battery change is now out of the way. Fingers crossed for a positive conclusion.
Thanks again.

 

Keep us informed, an interesting one!

 

Alarm went off again last night so the Hard Reset did not cure the problem.
In order to get one night uninterupted sleep I put the car in a secure place, closed it all up and left it unlocked for the night. This morning the boot lid had released again so it is definately this that is setting off the alarm.
Just had the battery checked out and it passed with flying colours.
Back to the drawing board I guess.
1) Does the boot release go through a relay and could that be faulty ?
If so, any idea where it is located.
2) Is there a micro switch that senses that the boot is open or is it a switch on the latch itself. I need to do some serious reserch before I start taking things apart.
3) Is there any way to lock the car without the alarm enabled ?

 

The trunk solenoid is driven directly from the security and locking control module.
The finger is beginning to point at the SLCM - it puts +12V on the solenoid so something simple like the solenoid harness shorting to ground wouldn't open the boot.
I don't know this model, on the XK series the SLCM is very susceptible to moisture damage but yours is, I believe, differently located.

 

try locking the car, then put the remote in a tin with the lid on. it may be the boot release button on the remote. alternatively take out the batteries after locking car. had a ford do similar and was a stuck microswitch in remote. a bit of switch cleaner sorted that.

 

Good idea but would an unlock via the fob set the alarm off with this model ?

 

this morning had to unload my boot and used the boot release button to undo the boot, got called away and left the boot open. about 5 mins later the alarm went off... unlock the car with remote all ok. tried it again out of curriosity after seeing this thread and again after about 5 mins the alarm goes off...just looked in the security system booklet and no mention of this feature. hey try it on yours.... mine might just be wierd???

 

Just tried leaving the boot open (opened with the fob) for 10 minutes - no alarm but a different model.
Andrew - if you put your car details in your sig (top left user CP?edit signature) we can easily see what you've got.

 

sorry about that. should be done now. by the way its a 98 xjr, saphire blue/oatmeal

 

Well maybe an XJR thing ?

 

I was thinking the same thing about the FOB. Try removing the battery for a night and see if it still happens.I reprogrammed my Wife's New Beetle to roll up and down windows using the FOB. A couple times, I'd come out in the morning to the windows down. One time, it was pouring rain.Come to find out, where I sat at my desk was close enough to the car and the button would be pressed and held while in my pocket, thus rolling down the window. I've also experienced sticky FOB buttons that can be fixed with some rubbing alcohol.It's cheaper to check this first before the security module, then if not, chase the SM.