I have a 2001 XKR Coupe. For several months, occasionally (and more often more recently) it will go into neutral when driving - particularly with torque. Doesn't seem to matter what gear. It will stay in neutral until back down to ~32mph then will engage normally again. Also see various messages sometimes (Engine Failsafe Mode (but no degradation of power / performance?, ABS, , ,).

I took it to my 'usual' shop and he replaced the actuator cable. No change. I took it to another shop and so far they've done small things (made sure all the ***** were in the ......, changed out the wires from the computer, checked the wheel bearings, replaced the rear tires,, ) no change. Now they're talking about R/R the transmission.

Only thing that bothers me; all the gears work as new - it shifts smoothly - no excess noise - the transmission seems fine, but there's something causing it to go to neutral.

Car has ~125K miles. Runs great.

Any ideas ?

 

Obviously you are investigating the J-Gate Gear Stick module but, at the age & mileage of the car, do you have any history of when the transmission fluid was last topped up and/or changed. The fluid could be past it.

 

You NEED to read the codes. All these systems have built-in diagnostics. You need to have the shop hook up a Jaguar/Land-rover aware scan tool and get the car to tell you what is wrong.Once you have codes, you can then start searching for prior occurrences on his forum or others.

The way automatic transmissions generally work is that fluid under pressure (controlled by solenoid valves) is applied to various clutches at a given time. These clutches control the various parts of a given planetary gear set. The overall gear ratio is provided as the net effect of whatever clutch are held vs. whatever other clutches are released. If the car appears to go in "neutral", it means a clutch that should "hold" is actually not. I believe it is called a "flare". The immediate cause can be a failed solenoid (solenoid itself, wiring, TCM, etc.), or a failed/worn clutch. As the car seem to recover and work fine for a while, it seems likely the clutches are fine. A large part of the logic is controlled by the road speed input, supplied by the ABS system which obviously need to be in order. The early XKRs have the Mercedes transmission, which is known to be very strong. The only issue I am aware of is a tendency to develop leaks in that cable area. It can apparently be fixed fairly easily.

PS: If you had a leak, has the fluid level be checked?

 

My guess is low fluid or low fluid pressure. You will need to take it to a competent shop for proper diagnosis.

 

I dealt with a similar issue on my wife's car that drove me nuts. Everything would be fine, then bamm, no gears. I did all the simple things to no avail (valve body, servos, sensors) , and the trans shop could offer no advice other than, "tear it apart."

Well I did, and the problem turned out to be a broken sprag. It would sometimes find a sweet spot and grip, and other times not at all. It most often failed when accelerating after coasting.

​​​​​​It affected 2 gears on her car that were related to the particular drum sprag that failed.

Good luck with your diagnosis and repair!