Mercedes-Benz W203 Light sensor message and rain sensor
What causes the Light sensor, visit workshop message on a W203?
The message means that the connection between the light and rain sensor and the roof light module is broken. The usual cause is the module's circuit board, damaged by water because of blocked sunroof drain tubes. The repair is replacing the module.
What else can be behind the connection fault?
The sensor cable can get pinched or break when the roof unit is reinstalled. The rain sensor's three wires run through the rear-view mirror to the roof unit, and they can be measured with a multimeter. The check is best left to a workshop.
Does my car have a rain sensor?
Look at the windscreen: the left sensor is the light sensor and the right one is the rain sensor lens. If there is a black plastic plate at the lens, the car has no rain sensor. The factory option code is 345; if it is not found on the vehicle data card, the sensor is not fitted, and replacing the glass does not add one.