Car (1999 Xk8 ) drives perfect if you leave shifter in Drive
but if you move it to the other side and use 2-3-4 it will go into low power mode
and gives you a "gearbox fault" , put it back in Drive and all is well again and drives just fine.
Tried doing a search on here but didnt find any results for this situation.
Not a big deal,more curious than anything what could cause this.

 

The selector lever operates a microswitch in the J gate when it's moved from D to 4. Imaginatively called the D-4 switch. That could be at fault. After that the Rotary Switch or selector cables could be responsible. The associated fault code is P0706.

If you get the car running in fourth gear while in Drive, then select manual 4 and the fault occurs, that would suggest the D-4 switch as the Rotary switch and cables wouldn't be involved in that situation

 

I replaced the illumination assembly in my car, I accidentally switched the car into accessory with none of the connectors plugged in and got both the errors you mentioned. There are multiple connectors, maybe that's the issue?

 

Here’s a couple of pictures when I rebuilt my J Gate module in my 99 MY XK8. Relatively easy job, within the centre console, with no special tools needed. Pic shows the microswitch on the rotary thingie. Might just need a clean as it was particularly dirty inside my J Gate module.



View of disassembled module

 

Mine is working fine, but this is good to know. More great info from this forum. No wonder there is sooooooo many pages of subjects. TM

 

But noting you have a 2003 XK8, note that this rotary switch arrangement is on the a 4.0 l XK8 and is different to the linear switch arrangement on your car.

 

David , is there a quick reference on how to remove cover for the console, I have electronic cleaning spray
if I can get top off should be able to spray it see if that clears it up before taking it apart.
Thanks!

 

A previous eminent Forum member has a lot of X100 Youtube videos. Check them out on his sam1174 channel. Relevant link below

 

And here’s a link to Rev Sam’s Youtube video on the centre console removal.


After you’ve done it once, it’ll only take you 10 min for entire job.

 

Thank You!