Mercedes Auto Lamp Function Inoperative

You get into the car and start your Mercedes-Benz. Next, you are greeted with an “Auto Lamp Function Inoperative” error message on the dashboard. A Mercedes-Benz light sensor malfunction most often causes this problem.

What does this mean?

If you are getting the Auto Lamp Function Inoperative error, it means that:

• The low beam (headlights) will not turn on automatically.
• Your windshield wipers will not turn on automatically if it rains.
• The auto lights function may stop working.

It doesn’t mean that your lights won’t work. When turned on manually, they will work fine, but will not turn on automatically. Also, your lights won’t turn on if you enter a tunnel. You will have to turn the lights on using the light switch.

If it starts to rain, don’t expect the wipers to start working automatically. Use the wiper switch to turn them on.

Common Causes

If you’re experiencing the “Auto Lamp Function Inoperative” error in your Mercedes-Benz, diagnosing the issue accurately can save you time and money. The YOUCANIC Full System Scanner allows you to scan all control modules, including the SAM (Signal Acquisition Module) and BCM (Body Control Module), which control the light and rain sensor functions. With the YOUCANIC scanner, you can read specific fault codes related to the Light and Rain Sensor (LRSM) and even monitor live data to determine if the sensor is sending proper signals. Instead of blindly replacing parts, use the YOUCANIC scanner to pinpoint the problem, reset the error code, and confidently restore your Mercedes’ auto light and rain-sensing functionality.

The most common cause that triggers the Auto Lamp Function Inoperative message is a defective Light and Rain sensors (LRSM).

This sensor is mounted at the top of the windshield (right in front of the rearview mirror).

You can save money by purchasing the Rain and light Sensor online and installing it yourself. The procedure is very simple and takes less than one hour.

You may notice that the error disappears once the car warms up. This is because the light and rain sensor mounted at the top of the windshield returns to normal operation once the car’s temperature increases.

If your car is under warranty, take it to the Mercedes-Benz dealer to get it fixed free of charge. If the vehicle is out of warranty, you must get a replacement Light and Rain sensor that fits your car. The best thing to do is to remove the old sensor and get the part number from it. You are looking for a part number that will look something like A204 870 47 26.

Then go online and search for Mercedes Light Rain Sensor.