Headlamp: Description and Operation

HEADLAMPS

The headlamps may be turned ON 2 different ways. First, when the driver places the headlamp switch is placed in the ON position, for normal operation. Second, with the headlamp switch placed in the OFF position, for automatic lamp control (ALC). During ALC control the headlamps will be in day time running lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions.

For low beam operation, battery positive voltage is applied at all times to the coil and switch side of the low beam relay in the underhood fuse block. Ground is applied at all times from G202 to the headlamp switch. When the headlamp switch is placed in the HEAD position, ground is applied to the headlamps ON signal circuit to the body control module (BCM). When either the headlamp switch is placed in the HEAD position or ALC is enabled, the BCM applies a ground to the low beam relay control circuit. This energizes the relay and applies battery positive voltage to the LEFT and RIGHT low beam fuses in the underhood fuse block. Battery positive voltage is then applied from the fuses through the headlamp supply voltage circuit to the headlamps. Ground is applied at all times to the left headlamp from G101 and to the right headlamp from G100.

For high beam operation, battery positive voltage is applied at all times to the coil and switch side of the high beam relay in the underhood fuse block. Ground is applied at all times from G202 to the headlamp dimmer switch. When the dimmer switch is placed in the HIGH position, ground is applied to the high beam signal circuit to the BCM. The BCM then applies a ground to the high beam relay control circuit. This energizes the relay, and applies battery positive voltage to the LEFT and RIGHT high beam fuses in the underhood fuse block. Battery positive voltage is then applied from the fuses, through the high beam headlamp supply voltage circuit to the headlamps. Ground is applied at all times to the left headlamp from G101 and to the right headlamp from G100.

For flash-to-pass (FTP) operation, when the headlamp dimmer switch is placed in the FTP position, ground is applied from G202 through the headlamp dimmer switch to the flash-to-pass signal circuit to the BCM. The BCM then turns the high beam headlamps ON as long as the headlamp dimmer switch is in the FTP position.

If the headlight 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.