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Are there any other problems with your 2003 XK8 that may be related to the issue.
With your gearbox, there's a computer dedicated TCM module, which will report any problems via the OBD2 port, which is linked by a CAN bus network to other control modules. You'll need a high level reader, not a simple one, so I suggest you find a garage with the correct software (SDD???) who can do this. Report back here with the DTCs they find.
Without these, you'll be guessing at the solution, and that'll be an expensive way to go and waste alot of time. It could be a number of things some simple and some hard. For example, it could be that the wheel sensors are no longer reporting the speed or maybe the instrument cluster in the dash. It could be wiring problems in the CAN bus network.
Cosmo2020,
If there are no error codes then check the Brake lights are not permanently ON. If they are, (irrespective of Braking or not), then the Gearbox will not change up. Let us know.
Then it likely means your brake switch is out of alignment. There is a slider part of the trigger to maintain contact with the brake pedal peg. This needs to be adjusted. If the transmission controller "thinks" you have your foot on the brake, it will not upshift. The workaround is to switch the lever from (D) to (5) slowly back and forth to let the car upshift and get moving.
With the ignition in the OFF position, what is the voltage across the battery terminals when checked with a voltmeter? This is the very first test that should be done when attempting to diagnose any 'fault' with the vehicle to eliminate the battery as the cause. Guessing on a Jaguar becomes very expensive very fast, so start with the basics and eliminate the most obvious causes first.
The voltage should be at least 12.6 volts with the ignition in the OFF position when checked with a voltmeter. If the voltage is less than 12.6 volts, the battery should be charged for six to eight hours at 2 to 5 amps and retested. Should the voltage still be less than 12.6 volts, the battery is suspect and should be replaced prior to attempting any further diagnosis.
Many of the 'gremlins' chased on these forums are the result of a failing or weak battery.
Cosmo2020,
What you need to do is gonna be physically awkward due to tight access. I had to remove the driver’s seat when I did it. This works.
1. In Park, engine off.
2. Depress Brake pedal with a piece of wood jammed against something like then seat runner.
3. Fold away foam insulation to reveal Brake switch half way up pedal lever. I tore a small piece off !
4. With Screwdriver or sharp tool, press this white plastic bit towards the black round metal rod part of the pedal (towards direction of front of car). You will hear one or two clicks of a ratchet.
5. Remove wood. Re-install foam.
6. Test drive :-)
