Exterior Lighting Systems Description and Operation: Headlamps

WARNING: This page is about a different car, the 2003 Buick Regal and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.

The headlamps may be turned on two different ways. First, when the driver places the autolamp switch in the ON position, for normal operation. Second, with the autolamp 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 autolamp dimmer switch, the low beam or high beam circuit is then, depending on the position of the dimmer switch, connected to the autolamp switch. When the autolamp switch is placed in the ON position, it provides a ground path for the low beam or high beam lamps through G201. The autolamp switch also provides a input signal to the BCM in order to determine if the headlamps are ON.

During automatic autolamp operation in low light conditions the BCM will pull the automatic autolamp relay low, energizing it. When the autolamp 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 autolamp switch and the automatic autolamp 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.