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Hi folks,

I have had my 1998 XK8 for 2 years, over that time I have had an intermittent 'gearbox fault' warning, with code P0706. This usually clears itself or can be cleared with a basic code reader. Local garage could find nothing wrong and generally it drives fine. However the fault is now permanent, does not clear with either code reader or by battery disconnection. Needless to say it is hard to drive it as it defaults to 3rd gear. Any ideas? I have booked it in to a local specialist auto transmission garage that was recommended by my local garage, but that's not for a couple of weeks.

Hi Andy.
Sorry to hear your having problems with your XK8.
P0706 = Rotary switch and/or D – 4 switch malfunction. I have a TSB referring to P0706,here's the link:
https://drive.google.com/file/d/1R7-0fK ... sp=sharing
Feel free to download and then you can print the info to show your transmission specialist or have a look yourself.
Hope this helps you get it sorted.
Take care.
Andy

Overtaken on the way to the party, but better late than never
That fault code is often caused by a problem in the J Gate, either the D-4 switch the rotary switch or the selector cable adjustment. An indicator that the problem is in this area can be the non illumination of the R marking the reverse position on the J Gate on selecting reverse.
The Drive to 4th switch, operated when moving the selector from D to 4th or vice versa, is a standard microswitch that might have failed, come loose or lost its lever. This You Tube video might help

https://www.youtube.com/watch?v=qWUYZUwcq0A

and this TSB

http://www.jagrepair.com/images/TSB/307-01-1.pdf

Thanks both, useful stuff, going to explore a bit more tomorrow….

On further reflection..
With most issues involving D-4 or indeed Park-Neutral that I read about online, the fault comes up when the lever is moved. Mine comes up now as soon as 'system check' displays on dash, even before starting engine. Does this mean it is more likely to be the rotary switch itself or indeed the cable adjustment rather than one of the microswitches? I presume if it was the latter then the fault would only appear when the lever is moved?

ok, so today exposed the workings of the J gate, no obvious issues that I could see, adjusted the cable slightly but doesn't seem to have made any difference. Will hang on to let the specialist have a look.

From my armchair, my thoughts on the three potential causes are

Microswitch - these tend to work or not work. Intermittency is unusual other than in a dry solder connection or loose fixing. Low probability.

Selector cable only has one correct position that has to be established from scratch. I'd do that first as a no cost option!

Rotary Switch - I would make this favourite if the cable checks correct

Hi Andy,
Sorry to hear of your XK8 gearbox woes, I know how problematic this can be, I'm not sure if this will help but have you seen my post regarding Intermittent gearbox fault? By replacing the relay shown in the post fixed the problem.

Good luck.

Thanks both. Interesting on the relay, definitely worth a try, so will get one and give it a try.

Sadly swapping the relay has not had any effect, shame.

So, an update.

Car was finally taken in by my local guy, I decided not to use a transmission specialist as they didn't seem that interested due to age of the car. Meantime it had developed 2 more faults, stability and traction control failure with ABS light on. the latter was traced to a faulty wheel sensor, needless to say this had to be drilled out and replaced as bolt was stuck. The gearbox fault was indeed failure of the rotary switch. Luckily he had several used ones which worked, so fitted it and for now all is well, albeit I am several hundred quid worse off. At least he didn't have to buy a new rotary switch at about £700!

Now we wait for the next issue

Hi Andy.
Glad you have it sorted, hopefully the next issue is a long way off.
Thanks for keeping us updated, it is good know the outcome of these issues.
I don't suppose your local guy is Mark at YourJag.If so I've used his services for parts and always found him great to deal with .
Happy motoring and enjoy your car.
Take care.
Andy

Yes Andy it is, I hadn’t used him for a few years as he moved into selling parts over servicing, but he definitely knows his stuff, very impressed