I usually drive my car (2000 XKR coupe) most weekends, and then hook it up to a battery tender for the week. Last weekend, after I connected the tender and closed the trunk lid, it popped open again a few minutes later. I figured I'd inadvertently pushed the fob button, so then went through a comedy routine of closing it; putting my fob aside so I wouldn't knock it; watching the trunk open itself again; trying it without the battery tender plugged in; watching it open again; taking the batteries out of the fob, and bingo! That solved it.

So, I put fob #1 aside for later attention, and got out my other working fob, #2. All good again.

Fast forward to yesterday, when I opened the car to retrieve something, then used fob #2 to lock it. a few seconds later, it beeped and unlocked itself! Locked it again; unlocked itself. Took the batteries out of fob #2, and now it stays locked OK.

Thoughts:
- everything else works fine - no codes, no other electrical gremlins (dangerous talk, I know... :-)
- I searched the forum, and a few people saw lock/unlock cycling because of bad door lock microswitches, but I don't think that's my problem, because (a) it started with just the trunk, and not the central locking system, and (b) removing the fob batteries resolves it
- I'm guessing it's a problem with the module in the car itself - having issues with 2 fobs and 2 different locks would be too big a coincidence
- I had power-washed the car prior to the first occurrence with the trunk. AFAIK, I don't have any leaks, and don't see any moisture inside the trunk, but I'm wondering if some water got into the module; is that feasible?

Thank you for any clues anyone can give me!

 

Assuming the behaviour is exactly as you described, the problem is the fob(s), not anything on the car. I think I would take the fob apart and clean the button contacts, as perhaps you have moisture or dirt in the contacts causing these ghost unlock commands.

 

When the battery in my wife's 2006 XK8 gets old and begins to die, it has been known to pop the trunk open on multiple occasions. A new battery has always resolved the issue....

 

Thanks, both, for your suggestions!

@dibbit - I will definitely give the fob cleaning a try, although as I mentioned, it does seem like a suspicious coincidence that they both went wonky at the same time (fob #2 was previously stored away indoors). Still, worth a try.

@Jon89 - both times, the spooky behavior happened when the battery charger/tender was attached to the battery and powered on. Shouldn't the voltage have been within spec, therefore, even if the battery is beginning to die? (i.e. wouldn't the charger have provided enough power to keep the Jag circuitry happy?). This battery's 4 years old, FWIW.

cheers

 

And it is also a suspicious coincidence that this ghost behaviour stops as soon as you take the batteries out of the fobs. Batteries in or out should make no difference when the buttons aren't pressed.

 

No guarantee that a failing battery will not begin to throw spurious codes or exhibit other strange behavior (such as popping open the trunk) just because it remains hooked up to a battery tender....

 

Fair enough; new battery will be my plan B, after the fob cleaning. Thanks again @dibbit & @Jon89 !

 

When I opened up the fobs to clean them, I saw the problem...

I've always had issues with the fob buttons not working, so last time around, I tried some "bake in the oven" conductive coating and re-coated the switch membranes where they contact the board. It worked well for quite a while, but over time, it gradually wears and crumbles off, leaving conductive deposits on the board - which of course lead to the behavior I was seeing! (And I guess the breakdown was time-based rather than usage-based, which is why both fobs went awry at the same time.) @dibbit nailed it.

This was the final straw that convinced me to replace these touchpads with real tactile switches (write-up with pics here) - I'm much happer now, and no more ghost openings...