Huge thanks to all who offered advice on the 'engine starts but stops after two seconds' post, which most said was an immobiliser issue.  The situation has moved on. I gather that a battery that is not throwing out full voltage can cause all sorts of problems for the ECU/ECM.  In the end I put a new battery in. A couple of times then the car started but 'went mad' - no tacho, no speedo, no indicators, etc. but drove fine. Then it had a day when all was exactly as normal - I started it four times during the day and drove about 40 miles in all to ensure the new battery was full charged, and I assumed it had fixed itself.

 

Next morning, back to the main problem.  No binnacle lights come on when I open the door.  Warning lights come on when I turn the key - including brake warning light with three beeps. Engine turns and starts and dies in one or two seconds. Has been the same for four days now

 

When it was running  okay, I went to a friend who has a diagnostic gadget - he plugged it in but it showed no faults.

 

Any thoughts appreciated, thanks

 

 

I would say you have some kind of drain on the battery when not in use.

 

How lively does the engine crank when trying to start?

What diagnostic "gadget" was it?

 

A generic OBD2 device won't tell you much whereas something VAG specific like VCDS might

 

Where are you based?

Thanks - MicMac the battery cranks the engine fine.  I'm just wondering, as a new battery, if it is yet up to full voltage, and if that could be affecting the electronics.

 

langers2k - thanks - sadly I am in Kent, so not nearby - but you are right it was a generic testing kit and not a VAG one

Okay that eliminates my theory...

 

Best get a proper scan for any pointers or go whole hog and arrange an auto electrician to have a look.

 

Try banging on the dashboard above the clocks, it may be a failing solder join or loose connection.