Headlamp: Description and Operation

The headlamps consist of two interchangeable single filament bulbs which provide high and low beams. The lower bulb in the headlamp is the high beam and the upper bulb is the low beam. These bulbs are also used for the daytime running lamp function.

The headlamps may be turned on in three different ways:
^ When the headlamp switch is placed in the ON position, for normal operation.
^ When the headlamp switch is placed in the AUTO position, for Automatic Lamp Control (ALC).
^ When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a six second delay.

During ALC control the headlamps will be in Daytime Running Lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions. A HEADLAMPS SUGGESTED message will appear on the Driver Information Center (DIC) when the headlamps and park lamps are off due to all exterior lighting controls being inactive when nighttime conditions are sensed. The message will also appear if the wiper activated headlamps feature is off due to the twilight sentinel being off, but the windshield wipers are on. The Dash Integration Module (DIM) provides battery positive voltage to the signal circuits of the headlamp switch. The signal circuits include the Head Lamp Switch input, and the Flash to Pass Switch.

With the headlamp switch in the ON position, the headlamp switch signal circuit is grounded through the headlamp switch to G201. In response to this input, the DIM provides ground to either the HDLP LO BM relay control circuit or the HDLP HI BM relay control circuit. The position of the dimmer switch determines which relay coil has ground. The DIM supplies battery positive voltage to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to both relay switch circuits.

When the low beam relay coil is energized, current flows through the HDLOBML fuse and the HDLOBMR fuse to the low beam headlamps. The low beam headlamps have ground at G402. When the HDLP HI BM relay coil is energized, current flows through the HDHIBML fuse and the HDHIBMR fuse to the high beam headlamps. The high beam headlamps also have ground at G402. When the headlamp dimmer switch lever is pulled toward the driver, the Flash-To-Pass switch closes. This grounds the DIM Flash-To-Pass input. In response to this input, the DIM energizes the high beam relay. Both high beams remain on until the driver releases the switch handle. If the low beam headlamps were on during Flash-To-Pass operation, the low beams remain on. The headlights may be switched to high beam with the opposite movement of the dimmer switch lever. If the headlamp switch is left in the ON position, the inadvertent power control feature will turn off the headlights 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON 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 turned off or the battery runs dead.