Transmission limp Blues

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Have spent the last year waiting for my mechanic to fix my 94 XJ40’s transmission problem. A new valve body and relay seemed to do the trick but not for long.
Here’s what’s up. Back in limp mode again. As I stated at the shop I felt the idle was too high at 1200 RPM. So if I held my foot on the brake when stopped, car in drive, the transmission would engage hard and go to limp with the dash light coming on. The best way around the situation was to slide the car into drive with my foot off the brake. Nursed it back to the 120 mile to home this way without problems.

Today I took the car out forgetting about the quirk and accelerating from a stop sign. I was back in Limp with the dash warning light on. Returning home got out the open end wrench and adjusted the throttle cable to zero tension. Still 1200RPM. Turned down the injector idle 300 digress and RPM was down to 825. One result of the slower engine speed was that transmission fluid now appeared on the dip stick up to the full mark. But the car is still in limp mode. The dash warning light stays on. Even turning off the key for an extended period of time does not extinguish it. It will go out if I disconnect the battery for a while. But was soon as I start it up, put in in gear, and then step on the brake It’s back to limp. Any suggestions?

There have been posts regarding the wiring harness that travels over the transmission getting trapped and a wire rubbing causing this?
My ‘40 would go into limp mode under (really) hard acceleration, never solved it but I never looked at the wiring harness and then sold the car.

The Jaguar PDU will communicate with the TCM but I doubt you will find someone with a working unit. (I wish I had the one I used at the dealer 20 years ago)

My guess would be the TPS. The engine uses 3 wires and the gearbox uses the other 3 wires.
Have you tried a replacement TPS?


Worst case would be to use the three wires for the trans and piggy back them onto the engine wires?

Jon, last time my car went to limp home mode, it was caused by a cracked solder joint in the TCM. There’s a relay in there and it should be checked to eliminate one problem area.

You should always check the ‘crappy’ blue relays as per the TSB Jaguar issued a few decades ago.

86-178A Inoperative Blue Relay.pdf (79.8 KB)