Buick Repair Questions? Ask a Mechanic for Answers ASAP
The headlamps may be turned on two different ways. First, when the driver places the headlamp switch in the ON position, for normal operation. Second, with the headlamp switch placed in the OFF position, during Daytime Running Lamp (DRL) operation in low light conditions.
The HDLP L and HDLP R fuse in the fuse block - underhood, supply battery positive voltage to both low beam lamps and high beam lamps at all times. The low beam and high beam circuits continue to the headlamp dimmer switch , the low beam or high beam circuit is then, depending on the position of the dimmer switch, connected to the headlamp switch. When the headlamp switch is placed in the ON position, it provides a ground path for the low beam or high beam lamps through G201. The headlamp switch also provides a input signal to the BCM in order to determine if the headlamps are ON.
During automatic headlamp operation in low light conditions the BCM will pull the automatic headlamp relay low, energizing it. When the headlamp relay energizes, it provides a ground path for the low beam or high beam lamps through G201, depending on the dimmer switch position.
Both the headlamp switch and the automatic headlamp relay can provide a ground for the headlamps for manual or automatic headlight operation. The headlights may be switched to high beam by pulling the dimmer switch handle toward the driver until the high beam dimmer switch is activated. When the dimmer switch is placed in the HIGH BEAM position, the indicator lamp and the high beam lamps are grounded and illuminate.
Most of the time I find that the multi-function switch has failed.A scan of the BCM might reveal a failure code that would help pinpoint this issue.View data of input switches & make sure they change with operation (headlamp,dimmer switch).