Headlamp: Description and Operation

HEADLAMPS
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.

AUTOMATIC HEADLAMPS AND PARK LAMPS
The automatic headlamps and park lamps are designed to automatically illuminate when the ignition is ON and the outside (ambient) light level is low as in night time conditions (night mode). Light levels are detected by the ambient light sensor, a light sensitive transistor that varies its voltage signal to the Body Control Module (BCM) in response to changes to the ambient light level. When the BCM receives a low light mode signal from the ambient light sensor it will then energize the park lamp and automatic headlamp relays illuminating the headlamps and park lamps. The DRL lamps will not operate when the automatic headlamps and park lamps are on.

In the low light mode, the ambient light sensor detects low light level, the BCM turns OFF the front turn signal lamps and grounds the park lamp relay and automatic headlamp relay control circuits, turning ON the headlamps and park lamps under the following conditions:
- The ignition switch is in the RUN position.
- The headlamps are OFF.
- The park brake is OFF (released).

If the engine stalls with the DRL in the low light mode, the BCM turns OFF the headlamps while the engine is being cranked. The park lamps will remain ON while the engine is being cranked.