Crasher, I've just measured the voltage at the cts plug with a cold engine I'm getting ~550 millivolts with sensor unplugged. Presumably that suggests ecu or wiring fault?
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Do the fans come on with the ignition and run at full speed?
Yeah they do.
The fan controller is seeing that the ignition is on so assumes the engine is running but it is not getting the temperature signal so it is programmed to go into emergency mode, it is highly irritating whilst trying to trace the fault and flattens the battery, I pull the fuse so I can concentrate. It could be wiring or an ECU fault I need to refresh my memory with the wiring diagram at work on Monday but I am booked solid so it may have to wait until lunch.
Thank you, much appreciated. There is no rush as I'm using my other mk5 currently. I wonder if the previous owner had done something when changing the battery as it's had a new one fitted before I bought it.