BMWs are packed with newer and newer technology every year, which can create a completely new list of things that may go wrong with the vehicle. One common problem with new BMWs is that the lights randomly switch on, but what is causing this to happen? Let’s discover why BMWs lights randomly switch on and learn how to fix them!
The lamp control module controls a BMW’s lights; this module receives information from the rain-light sensor. The sensor will then determine when the lights should be switched on or off in automatic light mode. A fault in either the lamp control module, rain-light switch, or light control switch will cause the lights to switch on/off randomly.
Read on to discover what may cause the BMWs lights to randomly switch on and what other light problems may be caused.
What Can Cause The Lights On A BMW To Randomly Turn On?
If a BMW’s lights are turning on randomly without any input from the driver, it could be a result of the following:
- Light Control Switch set to auto
- Faulty light switch
- Faulty LMC unit
- Faulty Rain-light sensor
Let’s go through these possible fault scenarios and try and identify which ones could be causing the lights to randomly switch themselves on.
The Light Control Switch
The light control switch on most BMWs will have four selections. These are:
- Off – The lights of the vehicle are off
- Automatic – The vehicle’s lights will turn on automatically when the light sensor detects low LUX (light) conditions.
- On – The light on the vehicle are on
- Parking –The Parking lights on the vehicle are on
The control switch settings are self-explanatory: on, off, and parking lights on. The automatic function can be a little confusing as to why the lights are switching on randomly. The automatic light function receives information from the light sensor behind the review mirror.
The sensor will activate (switch on) the vehicle’s headlight during low light conditions, such as dawn, dusk, nighttime, or even when driving through a tunnel or covered parking lot. In some cases, the sensor will activate the light on an overcast day or when driving past a building that may cast a shadow on the vehicle.
The light sensor’s sensitivity can be adjusted in the car’s setting menu if you are noticing that the automatic lights are too sensitive or not sensitive enough.
When the light control switch is set to the “off” position and the headlights continue to switch on randomly, one common problem is that the control switch is faulty.
A quick test will be to cycle through all 4 settings rapidly and then see if the headlight responds to the selections. If the lights are working correctly after this test, the fault may lay with the rain-light sensor.
What to do if you have a faulty light control switch?
Light control switches are an easy component to replace.
Tools you will need:
- Plastic pry bar
- That’s it. Just the plastic pry bar for most vehicles. But be aware that removal and installation can vary slightly depending on the vehicle.
To replace the light control switch, you will need to first remove the vent with the plastic pry bar or you risk damaging the light control switch. Once you remove this, remove the light control switch with the plastic pry bar. At this point, you just need to disconnect the switch from the wiring. Installation is just the reverse.
Below is a great video on replacing the headlight switch!
The Rain-light Sensor
The rain-light sensor is situated at the back of the rear-view mirror. The sensor uses an array of light detectors to determine the illumination (“LUX“) levels on the outside of the vehicle. This sensor is usually very reliable, but over time these sensors have faults like any other electronic component.
If the car has had a new windshield installed or had tint installed (I don’t recommend doing this on the front windshield but who needs to see, right?) it may also cause a random light issue.
The rain-light sensor sends information to the LCM (“lamp control module“). The LCM will then determine the correct light setting and switch the lights on/off. This will only work when the light control switch is set to automatic.
Below you can find a great DIY video on replacing the light sensor, it is a fairly easy replacement process.
The sensitivity level for the light sensor can be adjusted in the car’s settings menu. The sensor can be re-calibrated at a BMW dealer if the problem continues.
Lastly, there could also be a wiring issue between the sensor and the LCM but this is fairly uncommon.
The Lamp Control Module
The LCM (lamp control module) controls all the light functions for the car. In older cars, the wiring was much simpler and had a light bulb connected to a power supply and a switch with a wire. But with the advancement in electronics, BMW switched over to a centralized controller in the 1980s.
Not all BMWs will have the exact same LCM, and it is common to find different modules on the same BMW series as the options on the car may differ. The LCM also controls all the dashboard indicator lights, warning lights, and the odometer.
The LCM is another potential culprit if the vehicle’s lights are switching on randomly. The unit is located in the passenger’s side footwell and can be damaged if it receives a hard knock or kick. On BMWs equipped with sunroofs, water can leak through a damaged roof seal, trickle down the “A” pillar, and settle on the LCM. Water and electronics don’t work well together.
If the LCM is faulty, here are a few tell-tell signs:
- Headlights stay on when the vehicle is switched off
- Indicators switch on randomly
- High beams do not work
- Flashing headlights
- False dash warning lights
- Odometer display blank
If any of these fault signs are present on the vehicle, the first step will be rebooting the system. Rebooting the system by disconnecting the car’s battery will force all the systems on the BMW to reset. To reboot, disconnect the terminals from the car’s battery. Wait roughly 10-15 minutes before reconnecting the terminals to the battery. This is all that is needed to reboot the LCM. If the lights are still switching on randomly after the LCM reboot, they may need to be replaced.
The LCM can be replaced with relative ease, but the trick will be to purchase the correct module for the BMW. I would recommend purchasing a module straight from a BMW dealer or a reputable third-party dealer.
Replacing the module will require that you remove the passenger glove box, as well as a plastic trim piece. Replacement should take approximately one hour. Below is a great and quick video on removing the Light Control Module.
Conclusion
When the lights of a BMW are switching on randomly, it can be due to a faulty light control switch, faulty rain-light sensor, or a faulty LCM. The most common reason for the lights switching on at random is that the light control switch is set to automatic. This will turn the lights on and off when the vehicle detects low light conditions.
The good news is that issues with lights turning on intermittently are typically relatively simple to resolve and if you are mechanically inclined you can resolve the problem within a few hours.