A common problem in the Mercedes-Benz C-class (W204) is the poor performance of one of the rear-view mirrors, especially at high humidity (for example, if wet snow is wet). Since there is no fuse to heat the mirrors on the car, the problem may be:
- The unbreakable heating element in the mirror glass is most likely the collapse of the chain. This problem is not repaired, but is solved by replacing the entire glass.
- There's a problem with the transaction.
In any case, you should remove the mirror and test the entire circuit with a tester.
