Possible gearbox sensor? non starter

If you are happy the battery is actually holding 12.5v, then I guess the next place to try is both the engine grounds and the main engine fuse/relay box. Make sure any bolts/nuts are tight.

Is the starter clicking at all?

Hi,

checked grounds
checked fuse box

starter is not clicking.

No turning over, anything.

Do any of the instrument pack lights come on? Ignition lights, the red ones and the amber TC lights? You say gearbox fault gets shown on the display - is that right? Radio comes on?

Yes, lights all come on, radio, windscreen wipers, ignition lights etc.

There is a clicking under the driver's seat. sounds like a relay might be clicking.

Have a feeling its more to do with immobilising...will keep looking

Have you tested the starter, could be relay in fuse box gone too....

On the 2.5 diesels, if the gearbox overheat appears it usually means the settings are wrong within the Becm.

This can be caused by dodgy logics forgetting what it's meant to remember.

If you can get some diagnostics on the vehicle, swap the gearbox setting from auto to manual or whatever your vehicle is, & if this is the case then your EDC code will be wrong to. Usaully it swaps the engine to gems or changes the EMS code completely.

If you can get access to your becm settings, reconfigure the settings back to what it should be. If it changes the settings again then you need to look for a replacement becm.

Of course, i could be completely of track.