I have a 01 XJR with 93,000 miles. I get a gearbox fault light once in a while. It resets when I restart the car. The problem may happen a few times in one day or take a week to 10 days to happen. When the light is not on the car drives/shifts perfect. Very smooth. I could drive it 400 miles and no problem. When it does happen it takes place on very light acceleration from first to second. It feels like an aggressive shift and then the light comes on. Never had it happen with medium to strong acceleration. I did have the fluid changed recently after which the problem did not happen for a few weeks (which is not uncommon). I does not seem to be getting progressive, just once in a while. had the car for 6 years and only had the issue withing the last year. Took it to a shop to have the codes checked. P0715 (turbine speed sensor) and P1632 (can fault?) were the codes that were stored. He suggested to me to drive it until it gets worse as a rebuild would cost approx $4,000. I have never seen a transmission go bad in this way (great for a long while with an occasional issue). As I said earlier it drives perfect and shifts very smooth until the firm shift into second once in a while. No other issues. What could be the issue? Thanks for your help, Jerry

 

P0715 is an input turbine speed sensor error (according to http://www.aboutautomobile.com/DTC/P0715). This just might be the root cause of both faults. The other code, P1632, is "CAN Message Implausible". Usually, serial communications works perfectly or not at all. To me, an "implausible message" may have bad information in it, such as input speed data that is unstable or out-of-range. Since the problem is intermittent and the tranny usually shifts fine, it doesn't sound like your tranny is going to fail any time soon. Waiting for that to happen doesn't sound like a good course of action. I would seek a second opinion from a shop that has the tools to read real time data from the tranny control module and/or knows more about that speed sensor.

 

I had a similar peculiar "restricted performance" message in the window of my 2006 S-type. Since I wired with croc./alligator clips a 68,000microfarad at 16volt capacitor across my battery a few months ago, I've not had this. I thought it was my gearbox (ZF 6HP26) playing up as I was having issues with it at the time, but all box problems cleared up with new ATF and additives. I'm not saying this will cure yours, but it's so cheap and easy, it's worth a try. If you do try, make sure you have a 5amp fuse in series with the capacitor, you don't want a fire if there's a short. These capacitors are polarized being electrolytic, so see that the capacitor is the right way round. You're looking at only a few dollars here, so nothing lost if it doesn't work. Radio ham-shacks etc. are a good source if you can find one. If your not too brilliant at soldering, the Ham-shack might do it for you, and supply the croc. clips.
Leedsman.
Tasty looking motor BTW.

 

The merc gearbox is much easier to get serviced, have you had any transmission work done, any fluid or filter drains/fills?

 

I have a 2004 XJ8 I get the hard shift (like a thud) only going from first to second at low speed and when there is not any pull on the tranny (going down hill slowly) . It also seems that it does not have the response when I hit the gas and the mileage seems lower. I did have a Transmission Fault that I could not shift (it was cold and snowy) but cleared after being off for awhile. Is this an easy fix? Fluids? I did have a connector leak last yr and the dealer fixed it and said they filled the levels correctly. Any ideas?

 

I see that you are in Northern Va. And I Lived in Leesburg Va. and I used an independent trans repair shop in Purcellville that I have a great deal of trust in. It is Balsh Transmission Service 540.338.7447 and his name is Tom. He has rebuild my 99xk8 trans, rejuvenated my 95xj6 trans and replaced the fluid and filter in my 2000 s-type trans and it seems to tract better than before. He is a great guy and has proven himself to me. When you see him you are going to wonder if he can get into your car, he can. If you go tell him I said Hi!

 

I have a 2002 XJR and actually, I am at the Jaguar service center at Union Park Jaguar as I type trying to figure out what it is. Your lucky that your car threw codes. Mine is not even doing that! It does the hard shift, but does not put the tranny light on. But recently, I was really getting on the gas, and it skipped second gear completely and put itself into third, and then putting the engine in restricted performance mode. They cannot find anything wrong with it at all! I'm really stumped...

 

I have an 01 xj8 with identical symptoms. Did you ever get it sorted out ? Ahhh Charleston, we vacationed there every summer on Isle of Palms.