100% guarantee if the level's OK, it will be the sensor in the expansion tank. They corrode over tim and give dodgy readings. Mine was changed just before Christmas for the princely sum of £14.61. Took about 30 minutes to fit. Only ever seemed to fault when the temperature was really cold (never when it was warm).
3 months on, and having driven through December temperatures of -17°C, it's not come back on once. I also know 2 other GTI owners have exactly the same problem, also cured with a new expansion tank.
Hey matey, I spoke to VW Gilders in Sheffield the other day
asking for a sensor in the expansion tank and was told nothing
listed on the system
and that a new expansion tank
had no sensors that came with it
Where did you get yours from and what is the part number please
matey, the warning light and check coolant message comes
on all the time now and is doing my head in
any help would be appreciated,
Cheers,
Damo