I have a 2000 XKR convertible done 105k km. It occasionally drops into "Gearbox Fault / Performance Restricted" mode. In each case I just pull over when convenient; turn engine off; and its fine when restarted.

It first appeared when waiting at traffic lights and I'd slip it into neutral. After maybe half a minute or so, the warning light would come on. It took another couple of incidents before I figured out what was causing it, and hasn't been a problem since, as I now don't wait at the lights in neutral.
Until last night. There's a nice smooth roundabout (traffic circle) on the way home and there was little traffic, so I dropped it down through a gears under braking. I think it was when 3rd was selected that the Gearbox Fault reappeared with consequent very leisurely (almost non-existent) acceleration. Restarting the engine fixed the problem.

Would anyone have an idea what the root cause might be? Something simple and cheap I hope!

Thanks

 

I think the 2000 has/is pre ZF transmission so someone else my refute what I suggest,,, but what comes to mind for me is a STRETCHING cable or inaccurate positioning between the stick, the cable and the gear selector arm on the side of the box... On ZF transmissions, the 5hp, there is also a SICKLY expensive gear selector unit type thingy on the RH side of side of the trans BUT I don't think that's a thing for you...

See what others say.

 

I had similar symtoms /aggravations that you have stated. In my case, there was a faulty fuse connector contact that was intermittently creating a voltage divider circuit in which partial voltage dropped across across the fuse connector. In turn, this would then leave insufficient voltage across the TCM, causing my car to go into error mode. Finally, after many months of intermittent faults, it became permanent. (Thank goodness it was in my garage)
To my embarrassment (I have had training in voltage divider circuits), it took a week or so to trace the circuits due to my error of front probing the TCM instead of back probing the voltages.
Based on my experience, I suggest first checking / cleaning the 12v power feed and connections to the TCM. In my case, the culprit was in the under bonnet driver side fuse box. (LHD). When I cleaned that connection, all error codes dissappeared. ("Gearbox Fault / Performance Restricted" and/or "Incorrect part (module) installed")
I went ahead and cleaned all fuse contacts topside and all fusebox connectors bottom side (the culprit connection) since I had that fusebox unmounted.
This was in May 2013, and has been flawless ever since.

 

Your car has the Mercedes 722.6 gearbox also known as NAG1 or 5G-Tronic. The gearbox is used on many different cars, including Chryslers and obviously Mercedes. You will find lots of information about it if you google Mercedes 722.6 rather than just looking for Jaguar. You may well find someone with the same symptoms.

 

I think all 2000-2002 XKR's have the MB tranny.
An easy verification is to take a flashlight and mirror to count the tranny pan screws. (6 ct.)

 

@trainfan, what is the voltage across the battery terminals with the ignition in the OFF position when checked with a voltmeter?

 

Why not interrogate the TCM and find the relevant DTC(s)???

 

Bob, in my case, only the instrument cluster reported the errors. The CEL was always off and my Torque/Torque Pro did not report any problems. Can I assume that you are referring to a deeper interrogation?
Also, in my 1st post above, I forgot to state that I had swapped TCM's to no avail.

 

There are DTC's stored in the TCM if the GEARBOX FAULT MIL came ON.
ECM data will not always provide TCM codes.

 

Thanks Bob, both of my TCM's were apparently good. (I'm still running the original TCM)

 

The TCM will store DTCs in a 'non-volatile' area of the module.
Not all OBDII readers will interrogate the TCM.

 

Thanks for all the advice. I'll spend some time over the next few days investigating further.