aux fan at full speed.. help.

[Immune]

i have a BMW540i "E39", and lately i got the aux fan run at full speed once i start the engine
what would that be ?? any suggestions?????

[paulmessinared]

is your ac on?

[Seraph]

Full speed? I know when I start my car up the revs sit at like 1Kish until it gets out of blue and then drops to ~600 with AC on and ~400ish without AC. Out of control fan though could be a fan clutch failing which is bad.

[16valex]

It sounds to me that your auxillary motor controll speeds is broken.
It depends on the year, the auxillary fan motor speeds come with a resistor pack, and this resistor pack is known for going bad, I had to replace my wife's 97 528, the cost was around 70 dollars for part.

However, the later years I heard the speeds is controlled by the DME. You can test the speed of the auxillary fan by direct DC power to the connector to on top right of the radiator. The big brown wire is ground, and the rest are low, midium and high.

[Immune]

is your ac on?

No, it is just once i start up the engine, the fan goes mad and run like n airplane.