W204 Engine fan turns on with engine off! Help!

[Mikeden]

Hi there,

I have recently made the jump to Mercedes after a long line of BMW's and all was well until an anti theft display popped up on the screen and wouldn't let me start the car. After not being able to work out what was wrong, I disconnected the negative terminal on the battery for a few minutes and then re-connected it. This solved the problem and the car starts and drives fine now.

The problem now is since reconnecting the battery, the engine fan turns itself on about 1 minute after the car has been switched off and the key taken out. The fan quickly picks up speed to the extent that it is exceptionally noisy and will not stop unless the ignition is turned on.

Does anyone have any ideas whats wrong and how to fix it?

I have had to disconnect the fan and so am not happy driving it really. The only other thing to mention is that the car had been sat for about a month previous but had been started up and shut down again quite a few times when shunting it around on the drive. I wonder whether its damaged the battery? When I check voltage between the two terminals it was roughly 12.5v

Any help much appreciated - first foray into Mercedes not going so well at the moment....

Hi, just wondered what the eventual fix was with your car? I have a C250 and it has the identical problem to you, I have had two people look at it with no luck what so ever. I am not very mechanically minded but think if you could help with any info that would he great! I have it booked in at a specialist garage, but having read the threads, dont hold up much luck. My problem started after the battery was replaced, this due to the battery failing twice in one week. I now think this was probably due to the fan switching itself on after I had parked up and gone inside the house? Any help you can give would be greatly appreciated