Hi,

My first post as a new member.
I appear to have an unusual slant on the typical XJ8 Brake light posts ... but would be delighted to know it is a known fault and more so, of a known fix.
My X308 Sovereign has a build date of July 1997 ... one of the first off the line.

Recently during a Sunday afternoon drive, I got an Engine Failsafe message; then shortly after when ready to drive home I had to use the gear shift Park interlock manual release to get home, and once home established no brake lights.

Removing the CC40-4 plug from the pedal switch and shorting out pins 1 & 4 with a small jumper wire successfully actuated the brake lights, high level brake lights and shift Park interlock.

I reasonably concluded the pedal switch (and not the SLCM) had failed and ordered a new pedal switch from U.S. .
While waiting for the new switch to arrive, I had to move the car in the drive and so decided to again jumper the pedal switch lume to release the shift lever. This time, as the jumper, I used the twist tie off a bread loaf which was conveniently to hand.

When I went to move the car back again a short while later, the shift was again locked and upon inspection, the jumper wired had melted as if an underrated fuse.

A high current indication such as this aroused my suspicions and the more so after studying numerous circuit diagrams whereby it is confirmed that all the pedal switch does is give a ground / earth logic input signal to approx 4 Control Modules (Engine Control Module, ABS Traction Control Module, Security & Locking Control Module, Adaptive Damping Control Module) and ground the control coil of the high level stop light relay ... nothing that would generate a high enough current to burn my jumper wire.

The new switch arrived after 2 weeks and I optimistically fitted it and on a test run all was fine for about 10 minutes until the same Engine Failsafe message, no stop lights and no Park interlock activation ... alas the high current had burnt out a second pedal switch. (Stupid is doing the same thing and expecting a different outcome!)

I have removed the high level stop light relay to check if there might be a short between the power and control switching sides .... but no different ... I am still getting a formidable spark when I test the pedal switch lume with a short out jumper.

Basically ...something is errantly allowing for all intents a B+ battery feed into the pedal switch circuit ... tantamount to a dead short when the switch actuates.

So as far as I can surmise, it is either a damaged harness somewhere in the body, or one of the control modules is allowing power down what is supposed to be a signalling input channel and it could be any one of the four moules and not necessarily the SLCM just because it controls related functions ... which still seems to work.

Any clues would be most gratefully received.

 

I initially suspected what you did, it seemed quite logical. Not knowing exactly what the issue is since I've haven't had to deal with it, I'll go with basic electronics. I would remove all the brake bulbs and then test the system. My suspect is a possible bad solder joint at the base of one of the bulb sockets and may be shorting out on another or grounding to the body?
Have you tested it with the parking lights on?

 

This was recently posted and similar to what I was tellin' ya, its a good place to look.
https://www.jaguarforums.com/forum/x...brakes-165492/