987 Cayman Intermittent Non Starting

[Haves1979]

My brother has had his 987 Cayman for about a year now. Very occasionally (3 times in 12 months), it will not start - either from cold or when its been used. The starter turns, however the car does not want to fire. The car will display the message 'System Error - Visit Workshop' and then a variety of other different error messages. As well as non starting the car also won't open the front or rear hatches, and daft things like the spoiler will rise on its own.

It has been into a specialist who cannot find any errors or faults, including with the battery or the temp sensor(which can apparently cause this). They have recommended unplugging the ECU and disconnecting the battery to reset the ECU, which seemed to do the trick last time after it was left for a while. However, he's really looking to eliminate the problem has its a pain when it happens so any pointers appreciated

Cheers!

[Huskyman]

That really does sound like a duff battery tbh, as low voltage at the battery will cause lots of errors in the logic of all the control systems. I would be looking for stuff like bad earths from the engine and other stuff like that. I am suprised that the displays will show errors without fault codes being logged in the ECU. He may want to try a different specialist.
The simplest diagnostic that can be done is to get a multimeter and check the battery voltage and go from there, measure the resistance of the grounds.

Usually when you do a diagnosis the software in the diganosics will establish comms with all the different modules and give their status. When the car starts doing weird things it is usually the battery is giving out insufficent volts(around 13v DC) or there is a poor ground.

[Haves1979]

Cheers, yes it is a strange one. The battery was tested and it is apparently fine, although there is no harm in trying a new one. The other thing is the starter turns fine it's just like the car doesn't want to fire, or no fuel etc obviously plus the error messages.