The light control module (LCM) controls the different lighting systems in a car, including the headlight, tail light, turn signals, fog lights, and horns. It does so by using a central microprocessor-based device that manages and controls the lighting systems.
Besides centralized control, other functions of the LCM include automatic adjustments, improved energy efficiency, and fault detection.
For just one example, on a 2000 Crown Victoria, the lighting control module (see photo) is described this way:
The LCM is a microprocessor- based module that controls several vehicle subsystems. It responds to electrical input signals from various switches, sensors, and external modules.
The LCM is a microprocessor- based module that controls several vehicle subsystems. It responds to electrical input signals from various switches, sensors, and external modules.
– Richard McCuistian, ASE Certified Master Automobile Technician
Crown Victoria LCM subsystem functions include:
The LCM’s algorithms can automatically adjust the lights based on external conditions. For example, some LCMs might brighten the headlights if the road ahead is darker than anticipated. This makes driving safer because you won’t need to manually adjust the light.
The caveat is that not all LCMs work the same way or have the same functions.
In the same vein as automatic adjustments, the LCM can dim or turn off the lights if necessary to reduce unnecessary energy consumption.
You might also see a decrease in fuel consumption because turning on the lights results in more load on the dynamo, the component that converts energy from engine fuel into electrical energy.
LCMs on modern cars can also detect faults in the lighting system. For example, the LCM could alert you if a bulb is burnt out by showing “left/right side light out” bulb lights on your dashboard.
Knowing whether your car bulbs are working properly is crucial, especially on difficult terrains and low-visibility scenarios. If the LCM detects that one is faulty, you can change it before going on a trip, ensuring you get optimal visibility when you drive after dark.
Some signs of a failing LCM include the following:
These are all light-related issues. As such, they don’t always correlate to a malfunctioning light control module. For one, the bulbs of the listed lights might have simply gone out or the dashboard itself is damaged.
However, it’s still worth listing the LCM as the potential cause of problems. In some cases, resetting or replacing the LCM can resolve.
There are two ways you can reset the LCM: by manually resetting it or using an OBD scanner. Before doing so, check your owner’s manual for specific instructions, as resetting the LCM may vary depending on the car model.
You must also ensure the battery is fully charged for a smoother reset process. Lastly, disconnect any aftermarket lighting accessories to avoid interference during the process.
To manually reset the LCM, follow the steps below:
If the lights are still not working, consult a professional, as they’ll have more knowledge and experience dealing with LCM issues.
If you have an OBD scanner on hand, you can use it to reset different modules, including the LCM. To do so, follow the steps below:
If resetting the LCM doesn’t solve the issues, it might be better to replace the old module. To do so, follow the steps below:
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.