I have a 2001 (51 plate) A4 1.8T, recently the ECU light came on and VAG-COM reported an error similar to "Engine cooling mapping out of range
(probably a temperature sensor or themostat)", unfortunately I stupidly cleared the error by accident and didnt note down the diagnostic code. The
temperature gauge on the dash now rides at about 75C when it used to ride bang on 90C. In the last two days the ECU light has not come back on.
Basically, if the ECU does not come back on, is this something I should be concerned about, if so what is the most likely cause for the fault?

Yours, stupidly,
Milky.

 

I would start with the temperature sensor as it's pretty darn cheap. From there you would check into the thermostat.