Headlamp: Description and Operation

HEADLAMPS
The headlamps may be turned ON 2 different ways. First, when the driver places the headlamp switch in the HEAD position, for normal operation. Second, with the headlamp switch placed in the AUTO position, during operation in low light conditions.

On vehicles with manual headlamps, the LH HDLP and RH HDLP 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 through the fuse block - underhood, through the body control module (BCM), and to the headlamp switch. The low beam or high beam circuit then, depending on the position of the dimmer switch, continues through 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 G203. The low beam and high beam circuits are monitored by the BCM.

On vehicles with automatic headlamps, the LH HDLP and RH HDLP 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 through the fuse block - underhood, through the BCM, and to the headlamp switch. The low beam or high beam circuit then, depending on the position of the dimmer switch, continues through the headlamp switch. The low beam and high beam circuits are monitored by the BCM. During automatic headlamp operation in low light conditions, the BCM will apply voltage to the coil side of the headlamp relay, energizing it. When the headlamp relay energizes, it provides a ground path for the low beam or high beam lamps through G203, depending on the dimmer switch position.

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 daytime running lamps (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.