Pre-Heaters

[philmax]

Does anyone know about the pre-heaters in the cooling system. There are three heaters in the line from the rear of the engine to the heater matrix. I dont seem to have power going to them. How should they work? Should they come on when you start from cold then go out at operating temp. Is there a delay from starting the engine for them to come on. I might just put the meter across them for a while rather than starting then testing and then giving up.

[Crasher]

They are controlled by the engine ECU and can be tested using a diagnostic computer in output tests, what VAG call “Final Control Diagnosis”. Which year and engine code is your car?

[philmax]

Its the last half of 98 and the engine code is AHU.