Circuit Description

The Daytime Running Lamps (DRL) are designed to automatically operate exterior lights depending on outside light conditions.

The DRL operates in 2 modes:
^ The day mode
In the day mode, the BCM turns ON the high beam headlamps at a reduced intensity when the headlamp auto control ambient light sensor detects daylight under the following conditions:
- The ignition switch is in the RUN position.
- The headlamps are OFF.
- The park brake is OFF (released).

^ The low light mode
In the low light mode, the headlamp auto control ambient light sensor detects darkness, turning OFF the high beam headlamps and turning ON the low beam headlamps.
Additionally, the headlamp auto control ambient light sensor turns ON the following lamps:
- The park lamps.
- The sidemarker lamps.
- The license lamps.
- The tail lamps.

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 BCM turns ON the following lamps:
^ The side marker
^ The park lamps
^ The license lamps
^ The tail lamps

The following lamps operate in the usual manner:
^ The headlamp.
^ The instrument panel lamp dimmer switch.

B+ is applied contentiously to both the coil and switch side of the DRL Relay:
^ In Day Mode: The BCM applies a ground to the DRL Relay coil control circuit to the DRL relay. This energizes he relay and allows B+ to be applied through the high beam DRL feed circuit to the high beam headlamps in series. This illuminates the high beam headlamp at reduced intensity
^ In Low Light Mode: the BCM removes the ground from the DRL relay coil circuit. This disengages the DRL relay and allows B+ to be applied directly to the high beam headlamp allowing them to be controlled by the headlamp dimmer switch. The BCM then applies a ground to the headlamp relay coil control circuit and turns the headlamps on through the same headlamp control circuit as normal headlamp switch operation.