94 XJS V12 6.p L transmission LIMP Mode

My car has GM 4L80E transmission and it goes to Limp mode and light comes on dash. No codes thrown. Taken it to many shops and they can’t figure it out. Flushed transmission fluid few time with filter and no luck car is in MN 55369. Any help is appreciated. Thanks

Just a thought…

The same transmission was used on the '95-'97 XJR6’s, and several of them had issues with the electrical harness being too short. As the mount wears, this allows the trans to sag over bumps, tugging on the harness.
Maybe check that?

How did you check for codes? Unless you have a Jag PDU, you need to take out the tranny TCU, leaving cables attached, briefly short pin A8 to ground, and read blink codes from the warning light in the cluster with the ignition on Run, but the car not running. It will always blink code 12, 3 times, which just tells you its in diagnostic mode, then it will blink remaining codes 3 times each. Codes are below.

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Could be the Transmission Power Relay. Should be in a blue base, above the right rear wheelarch.


Sorry attached the wrong link. Here you go.


I took it to a local shop who had the PDU, they did not see any code.