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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4317
Experience:  Mercedes Benz Qualified Diagnostic Technician
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My car was sitting for a period with the windows open, over

Customer Question

My car was sitting for a period with the windows open, over 2 weeks unknown to me. The doors and carpets were very wet. The central locking is working, the electric mirrors and seat memory functions are all working as is the boot opening. all these functions are on the interior door panel. The electric windows switch to all windows including the rear isolator switch is not working.

Last night the 4 switches on the door were inop. All the doors separate switches were also inop apart from the front passenger switch. This morning I tried the passenger front and the window went down and now won't return

Can there be water in the switches and will they dry out and return to normal function. Can you tell me if the windows are fused separately and where the fuses are. I have the fuse diagram but ther is no mention of electric windows.

My car is a Mercedes E Class Elegance E270 CDI 2003 W211 Saloon Auto
Submitted: 4 years ago.
Category: Mercedes
Expert:  MB Paul replied 4 years ago.

The window motors are not fused as such - each door has its own Door Control Module (DCM) which gives power to the window motor when the switch is operated. The DCM acts as a kind of electronic fuse - if it detects too much current or a short then it simply switches off the power. Many electrical items work in this way now.

If water has got into the door then it could be a problem with the switch or even the drivers DCM

If the car was in our workshop then we would be testing communication with the drivers DCM and checking the signal from the switch using STAR diagnostic tool.

Even the switch is more complicated than a standard switch - there is only one signal wire between the switch and the DCM, when the switch is operated it sends a data signal to the DCM to say what switch is being operated.

Both the switch and DCM are possibilities if water has entered them, even if the water dries out it can quickly cause corrosion to the electronics inside the components.

Hopefully it is just the switch but to confirm this you really need it checked on a diagnostic tool.

You could also remove the door trim panel & check behind for water ingress to the DCM as well & try to dry out the switch & clean the contacts if required with some electrical cleaner. It would be difficult to say if this would be a lasting repair however & replacing the switch would probably be a more sensible solution.

Let me know if you need anything else.

Best regards, Paul