We have a 1997 C180 that always overheats (needle in red) when in queueing traffic. The Fan works OK when 12v is applied to it and the 40A supply fuse is OK. However when the engine is hot I can only measure about 2volts accross the fan and it is turning very slowly.

Is there a relay that could be defective - anyone know where it is?

or is there a fan control unit - anyone know where that is located ?

Thanks for any help...