Actually that doesn't seem bizarre to me at all. Ever since my first "module-ised" Jaguar (an XJ40, years ago) I've got into the habit of load-shedding as I get to the end of a trip, and always driving straight after any battery draining activity. For example, I always take the car for a drive right after washing and detailing it, because I know I've drained the battery. Both my XJ40s, my S-Type, my X308 and my X350 were all capable of going from cranking fine to the infamous 'click' seemingly at the drop of a hat.

 

Continuing to knock on wood. 10 days since I haven’t run the kitty in accessory mode, and she’s always started, Not setting alarm overnight night in garage. Driving at least every other day, and not using battery maintainer. Still using using the standard start procedure: fob in pocket, open garage door, open driver door,get in, put on seat belt, close driver door, press brake pedal, press start button, and she fires right up. Put top down. Wait until revs drop to normal idle, back out & rumble away.

I guess the real test now would be to run her in accessory mode for a while. Turn her off. And try to start the next morning. If the failure is not reproducible then she’s got some other demon.b

 

Another update…haven’t tried to leave the kitty overnite without starting it after running in accessory mode only. And I’ve yet to have a repeat of the starting issue.

 

Just FYI in both my XK’s a 12 XKR and a 13 XKR-S I get these codes for body control module, infotainment center A, even the cluster….

 

Well damn! Had a friend hook up a Obd tool to reset the TPMS codes, which is another story, and after running it on accessory for that…the kitty was up to her old tricks. It’s definitely not a low voltage issues, as the battery was recently load tested, and I get 12.5 volts at the engine fuse block.

Had to do the battery disconnect reset dance to get the kitty to purr again.

 

Hate to be repetitive but this is the battery being run down after having the car in accessory mode for an extended period. 12.5 volts is barely enough.

ps: why does your signature say your car is lunar grey?

 

12.5 volts is too low which explains your problems, either the battery’s the problem or something’s draining it.

EDIT: measure current draw with car turned on but engine not running, that’ll tell you if there’s too much load on the battery.

 

As mentioned above sometimes pushing harder on the brake pedal works. But what you want to monitor are the brake lights.
Do they come on when stepping on the brake pedal and the car is not starting?
Just another thing to check.
.
.
.

 

So, I posted this question on the Facebook “Jaguar XK8/XKR” page. And several people are having a similar issue, and their kittys seem to only get it to start after the battery reset dance. But, a few people made suggestions, that I tried as follows: (most agreed the brain or immobilizer gLes wonkers under conditions they have not sorted out, but most agreed this process seems to keep the kitty’s head on straight:

- set security after last use
- unlock to disarm security
- fob in range
- get in car
- close door
- press start button to turn on accessory mode.
- wait until everything comes up…a few seconds
- press brake pedal, then press start button
VROOM!

 

XKDreams,
You measured 12.5volts at a point in time, then assume that battery condition is fine after using Accessory mode for an indeterminate period.
Critical information #1 for system analysis is real-time voltage.
Please use a voltmeter similar to the attached and let us know what you find:




Typical inexpensive voltmeter from online vendor.



Without real-time data, we are all just guessing.

Best regards,
Bill