So, I came back to my car after dropping by a store today and it didn't react to anything electric. ignition, cabin lights, trunk, etc... almost like it was a dead battery.
I had a buddy come with jumper cables, and the second I attached them to the under bonnet terminals, everything started working again.... like it just needed to be reminded that it had a charge... I didn't even leave the jumper cables on when i turned on the car.
Now I'm just confused... Any guidance or experience with this issue?
Are there gremlins in the wiring? lol

 

I'm no expert, but sounds to me like a wiring connection issue type problem!


These type of things can just be so random, it can be difficult to find and leave you without a vehicle when you may need it most.


Good luck and hope to hear

 

The connections under the bonnet are known to have problems if they loosen and or become corroded. Check the power leads at the "false bulkhead connections" and at the fuse boxes, especially looking for any discoloration or other signs of corrosion, then tighten them, CAREFULLY so as not to break the small plastic insulator pieces.

 

Check the battery terminals, could be loose or dirty.
I'll bet a dime that's it.

 

Wait... we have terminals under the bonnet? Where are these?
My battery is practically inaccessible now, so this could be a huge help in the future

:edit: never mind, found this
https://www.jaguarforums.com/forum/x...solved-115858/

 

Follow the big black + wire back towards the firewall to find the "false bulkhead" connector.

(Of course, the XJ will look a little diferent under there, as the picture is of an XKR)

 

Speculating here but this is a weird one.

If the battery is in good condition and the leads are clean and tight, I think it could be due to the chip in the key head failing to pair with the Exciter Ring in the ignition switch. (this used to be a separate component on earlier models such as the XJ40 but looks to be part of the switch assembly on the X308)

This electronic 'handshake' unlocks the ignition sequence. If it fails, it's just like putting an unprogrammed key into the ignition - nothing happens!

Graham

 

Thanks guys, I've got a lot to start with here.

Battery terminals were pristine last I checked, but it never hurts to check and recheck again.

I've never checked the "false bulkhead connections", so that could be an adventure, but I'm putting my money on that needing some cleaning.

And last but not least, yes, I've had the issue with the key not wanting to do a proper handshake with the car. That issue only presents itself in freezing cold weather... which does make me suspicious of a general battery issue. It might just be time to replace the battery.

I'll hit all of these suggestions one by one as I have time this weekend and hopefully return with some answers.

Thanks!

 

Well, it hasn't happened again, yet... So that's good.
I went ahead and cleaned some rust off of the false bulkhead while I was out there today.
Note: when working with that nut, remember, it's hot... and when wrenches touch the body of the car, sparks fly. lol.
We'll see if the issue comes back... or until my next adventure... Thanks.

 

I may have overlooked it, but I don't think I saw a warning to not use the connections in the engine compartment to start the car in any of the posts. The owners manual has directions on jump starting and they should be followed to avoid damage to the modules.

 

I had a similar problem. Car would not start, no click, nothing. Call the wife to bring the jumper cables, touch cables to battery terminals and power comes on. The negative strap was very hot. It turned out the crimp on the ground strap was not making good connection. The battery terminals were spotless. Replaced the ground strap, problem solved.

 

The studs at the fuse boxes on the left hand side of the engine compartment are not ideal for the the purpose. This is because the cable daisy chains back to the high power fuse in the trunk before eventually going forward again to the false bulkhead stud on the right hand side.

On the other hand, in a pinch, the false bulkhead stud is ideal for jump starting. It terminates the cable leading directly to the starter which then daisy chains to the alternator output. From stud to starter is maybe three feet of very heavy wire. It also feeds the battery through the high power fuse. Thus, all systems will be getting juice.

The layout of the power distribution circuits showing the above can be found in the electrical diagrams in the earlier pages under "main power distribution".

 

Gille, follow the troubleshooting link in my signature and check all the connections.