How does a dimmer switch work on a light control module?

In modern electrical architecture, the light switch might signal the light control module to turn the exterior headlamps, marker lights and interior lighting on or off. In the same manner, the dimmer switch might signal the light control module to switch from the high-beam to the low-beam headlamp circuit.

Why is the left low beam brighter than the right?

Since both low-beams are powered by the same pole of the headlamp switch and the left low-beam is bright while the right is dim, the problem is probably not in the headlamp switch. Since the headlamps are individually grounded and each headlamp has one bright filament, the problems are not likely to be on the ground side of the circuit.

What happens when a headlight is switched on low beam?

When the headlamps are switched on low-beam, the daytime running lamp relay coil is energized and the relay cuts the voltage-dropping resistor out of the circuit, thereby operating the low-beam bulbs at full voltage.

What to do if there is no communication with a module?

If your scan tool indicates “no communication” with a specific module, then you must diagnose the reason for the non-communication. Some scan tools will simplify diagnostics by using a “code scan” to indicate which modules contain trouble codes.

Where does the ground for the headlamp relays come from?

The ground for the headlamp-relay coils is provided by the body control module (BCM), so to have any headlamp operation, the BCM must provide this ground. So even though we have two headlamp relays and separately fused headlamps, the BCM can still cause loss of all headlamp function.