How to Troubleshoot BMW Rain Sensor Malfunction?
2 Answers
To troubleshoot a BMW rain sensor malfunction, it is necessary to initialize the rain sensor and then conduct a test drive to resolve the issue. Working Principle of the Rain Sensor: The rain sensor utilizes an optical design where infrared light emitted by the LED is directed at the critical angle for total reflection at the interface between the windshield and air, ensuring all reflected light reaches the receiver tube. When raindrops appear on the windshield surface, the change in the air interface causes the light reaching the receiver tube to weaken. The larger and denser the raindrops, the weaker the light received by the tube. The wiper control unit adjusts the intermittent timing of the wipers based on the output signal from the receiver tube. Inspection and Analysis of Rain Sensor Malfunction: Press the automatic intermittent control button on the wiper switch—the green indicator light on the button should illuminate normally. Spray water onto the rain sensor area of the windshield to simulate rainfall, then turn on the wiper switch. If the wiper only makes a single sweep and stops, proceed to read the fault codes from the relevant control unit to diagnose the issue.
I've encountered an issue with the rain sensor malfunction on my BMW. Simply put, the wipers stopped working automatically. First, I would check if the sensor area on the windshield is clean, wiping off any dust or water stains with a soft cloth, as dirt can easily cause misjudgment. Second, restart the vehicle system, such as turning off the engine and waiting a few minutes before starting it again—sometimes minor software glitches are reset this way. If it still doesn't work, check the fuses in the engine compartment to see if any are blown, locating the fuse box for the wiper circuit and replacing them. Third, scan the OBD port to check for any fault codes; if you have the tools, reading the codes yourself can help pinpoint the issue. Finally, if none of these steps solve the problem, you'll need to visit a professional shop to inspect the sensor or wiring. Remember, keeping the windshield free of dirt buildup and performing regular maintenance can reduce such issues. If the sensor fails, manually operating the wipers is still safe—just avoid driving in heavy rain if possible.
