BMW E38 light warnings and light module (LCM)
Why does the E38 report a bulb failure even though all the lights work?
The cause is often the bulb socket: poor contact or a loose socket triggers the warning. Bend the contacts tighter, sand them with fine paper and clean them with contact spray. A bulb whose filament breaks intermittently can also give an occasional warning.
What is the LCM and where is it in the E38?
The LCM is the light module, which controls the car's lights and monitors them. It is in the front passenger footwell, on the door and engine side, under a plastic panel. A module fault can show up as, for example, rapidly flashing indicators, light warnings or the indicator starting by itself.
What other faults can cause light warnings in the E38?
Water in the module's connector or a corroded ground can cause the same symptom. The water can come from clogged sunroof drain tubes. Aftermarket LED lights may also not work with the car. A faulty module is replaced.
Why are the E38 brake lights on all the time?
Usually the fault is in the brake light switch, which is two-stage and is replaced with a new one. Another possible cause is the ignition switch base, and replacing it may also remove other symptoms, such as the interior lights staying on. Also check the brake switch fuse.