Ok, first-time Merc owner here. I purchased this vehicle about a month ago and the rain sensor for auto-windshield wipers is not working. Could this be a faulty sensor or maybe the fuse?

I noticed on the drive home from purchasing that the windshield wipers chatter when being used and during a hard rain after turning the wipers on, they only worked when turned past the dots (sensing settings). I put it on the first two sensing settings and neither worked with the increase of rain (just stayed off). What confused me about this is that during the rain storm, my dashboard displayed a message saying turn on headlamps. Isn't the rain and light sensor one in the same? Any help would be greatly appreciated before I go and replace something that isn't malfunctioning. Thanks in advance.

Maybe try calibrating the rain sensor first. I had my windshield replaced and had to have the sensor calibrated. Before calibration, the first two (dot) settings only worked as interval settings.

Not sure if the light sensor is the same, but I had no problems with auto headlights while my rain sensor was out of calibration.

Good luck!

Calibration might be the fix. I'm assuming a used car purchase here. If they changed the windshield, the rain sensor often needs recalibration.

Regarding the "turn on the headlight" warning, I think it's separate. Do you the headlight switch on "automatic?"

Sorry for the late response, but I am just seeing this. It is a used vehicle and I'm honestly not sure about the windshield ever being replaced. I'm assuming a calibration requires it being brought in for service? (stupid question, I know). Yes, I keep the headlight knob on auto.

Yes, you'll need to take it to someone who can talk to the GLC's computers. I'd price-shop the dealership, some glass shops, and any trusted independent Mercedes service shops in the area. In my case, the glass shop quoted $800 and the dealership quoted $300. (No nearby independent shops.)