So I'm sitting in my 2007 XK convertible - not using any electric - while my wife is picking up some groceries. She gets back to the car and the trunk will not open (we both have key fobs). I hit the trunk release dash button - nothing. I get out to use my key and notice that the dome light does not go on when I open the door, and the key fob button will not open the trunk. The car is completely dead. Pressing the start button does nothing.

I'm back in the driver's seat, on hold with AAA when I re-open the door and the lights go on. So I close the door, hit the start button and the car starts up like nothing was wrong.

Any ideas what the issue might be - I did search the forum for electrical gremlin issues like this, but did not find the answer.

 

Loose battery or ground connection?

 

I'd say Low Voltage. That's the main cause of any electrical issue.

 

Maybe it is a variation of this issue:

Situation: An issue has been identified where after returning to the vehicle less than 10 minutes after
locking, the customer is unable to unlock the vehicle with the remote handset and, after using the mechanical
key to enter the vehicle, the engine will not crank. After 10 minutes the vehicle will recover and operate
normally. This may be caused by a software issue with the Central Junction Box (CJB) and Auxiliary
Junction Box (AJB).

 

See this 11 year old thread, also a 2007:
https://www.jaguarforums.com/forum/x...t-start-47834/

And this thread from 2013, also about a 2007:
https://www.jaguarforums.com/forum/x...ressed-105382/

 

Hi U

Sounds like this could be the issue. Where is this quote from, and is there a recommended fix?

 

How many kilometres/miles are on the vehicle?

What is the age and condition of the battery?

What is the voltage across the battery terminals with the ignition in the OFF position when checked with a voltmeter?

 

It is from an early service bulletin (JTB00147). The fix is to update the firmware in the CJB and AJB so would need to be done by a dealer or someone with the dealer SDD tool.

 

Were you both carrying your Smartkeys at the time ...........?

Graham

 

Yes

 

I've had exactly the same issue, managed to get the passenger door open with the emergency key and was about to call the RAC out , tried again and it started.
Thought it might be a faulty fob so resorted in carrying both of them.
Thanks for the info we look into this further.

 

I have had this same issue on my 07 XKR, I found that disconnecting and reconnecting the battery will correct the issue, but that is a pain, another quick fix I found is if I momentarily short the battery to ground using the jump start post to a ground point will reset what ever is not completing the circuit.
It's not battery from what I can tell, all reading after sitting are good and this has happened several times after disconnecting my CTek after sitting over night.
Just my 2 cents.

 

??????????????????
SERIOUSLY???
Dang, I'd never do that. Jumper could weld itself to the connections and burn stuff, voltage spikes because everything is still live......
That's just a crazy thing to do! Sure, it may do what you want, but what about all the stuff it does that you DON'T want?

 

"...I momentarily short the battery to ground using the jump start post".

Should've included: "after disconnecting the positive terminal from the battery"...

 

OK, I get it, not the safest or most ideal method, and it may very possibly cause other issues , but it works. I would not recommend anyone try using this method either.
I'm leaning towards the software update being needed, as the battery is good and there is some circuit that randomly fails to connect/start. I've gone thru the schematics and don't see anything physical in line that would cause the issue, There has been no consistent conditions when this happens, short stop, over night with CTek connected, over night without CTek connected. and some times after using the key to get in the trunk without touching anything the alarm goes off and everything works. I've gone thru most all of the ground post locations and cleaned them along with the battery cables .
Stumped and it's not good when I walk out to the car and the door opens and I get no lights or any indication of life, it's strange that the door opens with the fob in hand but the window does not drop.

 

For new folks, disconnecting BOTH cables from the battery and shorting them together for a half minute or more is called a "hard reset" in the maintenance manual.

It's a normal procedure, useful if other things don't work to solve a temporary problem.

It zeroes residual voltage levels in certain electronics, usually returning certain conditions to default. It doesn't erase recorded codes, or reset radio presets. It will require resetting the window stops.