Low Beam Headlamps

WARNING: This page is about a different car, the 2022 Cadillac CT4. However, it is still accessible from the selected car via links, so may be relevant.

The headlamps may be turned ON in 3 different ways:

When the turn signal/multifunction switch is placed in the ON position, for normal operation
When the turn signal/multifunction switch is placed in the AUTO position, for automatic lamp control
When the turn signal/multifunction switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay
When the turn signal/multifunction switch is placed in the AUTO position, with the windshield wipers in the intermittent position, automatic lamp control may be delayed or not activated.

The Lighting Control Module (Lighting Control Module) will also command the low beam headlamps ON during daylight conditions when the following conditions are met:

Vehicle needs to be running or in service mode.
Turn signal/multifunction switch in the AUTO position
Windshield wipers ON
Vehicle in any gear but PARK

When the Lighting Control Module commands the low beam headlamps ON, the operator will notice the interior backlighting for the instrument cluster and the various other switches dim to the level of brightness selected by the instrument panel dimmer switch.

Low Beam Headlamps

The body control module (BCM) monitors three signal circuits from the turn signal/multifunction switch. When the turn signal/multifunction switch is in the AUTO position, all three signal circuits are open. When placed in the AUTO position, the BCM monitors inputs from the ambient light sensor to determine if headlamps are required or if daytime running lamps will be activated based on outside lighting conditions. When the turn signal/multifunction switch is placed in the OFF position, the turn signal/multifunction switch headlamps OFF signal circuit is grounded momentarily, indicating to the BCM that the exterior lamps should be turned OFF. With the turn signal/multifunction switch in the PARK position, the turn signal/multifunction switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the turn signal/multifunction switch is placed in the HEADLAMP position, both the turn signal/multifunction switch park lamps ON signal circuit and the turn signal/multifunction switch headlamps ON signal circuit are grounded. The BCM responds to the inputs by sending a serial data message to the Lighting Control Module, the Lighting Control Module then sends a pulse width modulated voltage signal to the headlamp assembly. The headlamp assembly responds by illuminating the respective LED(s). If serial data communication is lost between the Lighting Control Module and BCM, all Park, Tail, Low Beams and License Plate Lamps will default on with the vehicle in service mode.