3.6 V6 fault code U0100- ECM lost comms with PCM- reluctant to start and has no drive when it does

[RWG]

Title nearly self explanatory- my V6 Estate has been boring reliable until now when it suddenly failed to start, eventually did and that seemed to be that. It was due to visit my local garage for an oil change service so that would be getting checked out then. When the car was being picked up(my local garage does a pick up and was in fact bringing my motor home back to swap them over when it wouldn't start again and when it did reluctantly there was no drive when engaging D on the DSG. Car was eventually recovered to said garage. I read the fault code on an bobby basic OBD reader before it left and that has since been verified by their computer however they haven't been able to diagnose anything else either and suspect a broken wire or failed earth strap somewhere. We have had a cabin water leak that did for the electric heated seats two years ago so may be related. Any pearls of wisdom or guidance out there?

 

[chimaera]

I think the first thing to do is get it scanned properly with a VAG compatible scan tool to see if any other modules in the car are throwing communications fauIts. If modules are not talking to each other it's reasonably likely that there's a CANBUS problem or one of the modules is faulty. A full scan of the vehicle will shed some light on this.

[RWG]

By way of an update- because of the lockdown we don’t need a second car and it has been low priority for both me and my local garage. Long story short - diagnostics by a third party VAG set up didn’t reveal any clear cause and effect? Loss of communication with Engine Control Module is  still the reported fault. It has started after a batttery disconnect/reconnect and ran normally until it was stopped and it then refuses to start until the battery is disconnected again. my garage is suggesting sending the Engine CM away for testing to a specialist. Any pearls of wisdom out there? 

[ethel]

Hello, might sound like a daft question but as someone who owned a string of Italian cars for many years I got used to checking connectors on an almost obsessive level when things weren't playing ball electrically.

 

Have you/the garage checked/cleaned connectors on the ECU and associated componentry to eliminate those as potential failure points..?

 

Good luck with it anyway - please keep us posted.

 

Dave.

[RWG]

The latest update on this saga is that the engine ecu  was tested off site and confirmed okay. A local VAG specialist is now assisting my garage and has found no obvious faults( or his computer hasn’t) all relays and fuses have been double checked and he has now asked for the passenger front seat and carpets to be removed so that he can check the wiring harnesses in there. The only change in behaviour since these earlier checks is that the car will not start at all now even when the previous workaround of disconnecting the battery had always worked. When the car was capable of being started and running it was doing so without issue and faults. The said VAG man has been heard to mutter that car electrics are to complicated these days! He hasn’t apparently come across anything similar in his workplace either.