The Gem unit (general electric module),is situated above and to the right of the accelerator pedal.These rarely give trouble and i have never seen one with water ingress.The problem is more likely to be related to a door or tailgate "door open"contact .These are located on each door striker plate and on the tailgate door latch.

Okay. Thanks for the info. alot of the other posts said about the latches being the problem, where although the doors were closed the latch wasn't going in deep enough to tell the computer it was closed. How would I know if that was the case, or is it just trial and error. Is there a test I can do. I recently had a diagnostic test done for another fault and it wasn't picked up then, although at that time the light wasn't on and all was normal. It's hard because it is intermittent and not continuous.

The 'door closed' sensor isn't the latch, it's a little plunger somewhere on the shut surface, has a black rubber dust cover: take the cover off, take the gadget out and check the contacts aren't corroded/wire intact etc.