Your pride and joy, your means of getting around and probably one of the most expensive things you own, it can be alarming when things go wrong with your Mercedes-Benz. Of all the things that could happen unexpectedly, getting the Auto Lamp Function Inoperative or Auto Lights Inoperative error message pop up on your dashboard can be one of the most disheartening.
You're driving around, or have just gotten into your car, and suddenly realise that your auto light function isn't working and you have an error on your dashboard.
Warning message is common for all mercedes-benz cars with light and rain sensor fitted it includes - C-class W204 S204 C204 W205 S205 C205 E-Class W212 S212 C207 A207 W213 S213 C238 A238 S-class W220 W221 W222 GLC X253 C253 ML W164 W166 GLE C292 CLA C117 W117 Sprinter W906 Vito W447 and many other mercedes car models.
When this happens, you're probably wondering what exactly the error message means and what you can do to fix it. Will it be expensive? Can you fix it yourself? What causes the error in the first place and is there anything you can do to you avoid it? We'll answer all of these questions for you so you can get your Mercedes back up and running at its best in no time.
What does the error message mean?
Basically, when you receive the Auto Lamp Function Inoperative message on your dashboard, it means that you have a malfunction with your automatic lights. This error usually occurs alongside your low beam headlights not automatically coming on, the windshield wipers not activating automatically in the case of rain and even the complete cessation of operation with the auto lights function.
What is the auto light function and how does it work?
To understand the error, we must first understand the function of the auto lights and exactly how they work. It's worth noting that the auto light function works independently of the manual light function, so even if the auto functions stop working you should still be able to manually operate your lights and windshield wipers.
The automatic light functions on your Mercedes are connected to weather sensors (LRSM) that are placed on your car, just above the windshield. These weather sensors detect, store and analyse information such as the amount of light and moisture there is in the air to determine whether it is raining, dark or foggy.
Once it has this information, it sends a command to your windshield wipers or lights to come on and off as needed.
Why isn't it working?
The LRSM that picks up the light and rain readings may be faulty. The most common causes of the Auto Lamp Function Inoperative error are:
1. If you store your vehicle in a cold, dark place, the vehicle's LRSM (light and rain sensors) may have become confused as to what the conditions are and what you need once you start driving. The best advice is to drive the car normally, using the manual windshield wipers and light settings, and see if the problem resolves itself. Once the temperature in the car increases, you might find that everything works as normal, or it might take a little bit longer (up to one day) for the problem to resolve.
Usually we recommend to use mercedes-benz vehicle for few days and see what happens next, in mostly cases within 1-2 days it fixes itself, if not try to remove auto lights sensor from the windshield and install it back and usually it works but if even that doesn't work - the go to step two.
2. If the problem hasn't self resolved within about a day, it's more likely that your weather sensor has failed. If this happens, you'll need to have a new weather sensor fitted to your car in order to restore the automatic light functions. You can have this done for you at your local Mercedes dealership, or you can purchase the parts online.
Replacing the Light & Rain sensor
Replacing the Light & Rain sensor on your Mercedes isn't as complicated as you may think. In fact, you can purchase the part you need online and then fit it to your car yourself in as little as an hour. If you'd prefer to have the professionals take care of it, you can take it to your local Mercedes dealership. If your car is still under warranty, the new weather sensor will be fitted for free at your local mercedes-benz dealer shop. If not, then you'll have to pay for the parts and for the cost of labour.
Part itself usually looks like similar to these A1648203085 or A2048704726.
It's often cheaper and easier to just buy and fit the part yourself if you're outside of your warranty period. There are several how-to guides and videos available that can guide you through the very simple process.
If you choose to purchase the weather sensor yourself, you'll need to ensure that you find the right option for your car. The easiest way to ensure you get the right weather sensor size and type is to check the part number of your old weather sensor after you've removed it and search for the part online via that number.
