Operation CHARM: Car repair manuals for everyone.

Headlamp: Description and Operation

You can use the headlamps in two different ways.
^ Place the headlamp switch in the ON position for normal nighttime operation.
^ Place the headlamp switch in the OFF position for Automatic Lamp Control (ALC). During ALC the headlamps are in Daytime Running Lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions.

The DRL/EXT lamps fuse and the EXT lamps fuse in the top of the engine wiring harness junction block supply battery positive voltage to both of low beam lamps and to the right high beam lamp. The low beam circuit continues to the high/low beam switch then, depending on the position of the dimmer switch, connects to the normally-open headlight relay switch contacts. Placing the headlamp switch in the head position provides a ground path for the headlight switch input of the Body Control Module (BCM). After receiving this input, the BCM energizes the headlight relay. When the headlamp relay is energized, the low beam circuit is connected to ground G201. The high beam circuit is divided into a left and a right side circuit.

The DRL/EXT lamps fuse in the top of the engine fuse block supplies battery positive voltage to both the coil and to the normally-closed contact of the DRL relay switch circuit. During high beam operation, the left side current flow is through the closed contacts of the DRL relay, and to the left high beam lamp.

The EXT Lamps fuse in the top of the engine fuse block supplies battery positive voltage to the right high beam lamp. Both high beam circuits are then connected together, and continue to the dimmer switch. When the driver closes the high beam contacts of the dimmer switch, the circuit is grounded at G201. Both the headlight switch and the BCM provide a ground, or control circuit, to the headlight relay coil circuit for manual or automatic headlight operation.

When you place the headlamp switch in the OFF position, and the ambient light sensor indicates low light conditions, the BCM energizes the headlight relay for low beam operation. With the headlights in the low beam position, you may momentarily turn ON or flash the high beams using the dimmer switch handle. When you pull the headlamp dimmer switch handle toward you, the Flash-to-pass (FTP) switch closes, grounding the high beam circuit at G201. Both high beams will remain ON until you release the switch handle. If the low beam headlamps were ON during an FTP operation, the headlamps will remain ON. You may switch the headlights to high beam by pulling the dimmer switch handle toward you until the dimmer switch is activated. When the dimmer switch is placed in the HIGH BEAM position, the indicator lamp input to the BCM is pulled low. The BCM then sends a class 2 message to the instrument cluster in order to illuminate the high beam indicator lamp.

If the headlamp switch is left in the head position, the inadvertent power control feature will turn off the headlights 10 minutes after you turn the ignition switch to the OFF position. If you place the headlamp switch in the head position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain ON until you turn them OFF or until the battery runs dead.