Daytime Running Lamp: Description and Operation

The LO Beam Headlamps are automatically controlled by the Daytime Running Lamps (DRL) Control Module. With sufficient light, the DRL Control Module will activate the LO Beam Headlamps at a reduced intensity. With low light conditions, the DRL Control Module will activate the LO Beam Headlamps at full intensity. If the DRL System is inoperative, the Headlamp/I/P Dimmer Switch overrides the DRL System to provide manual control of the Headlamps. If the Park Brake is set when the Ignition Switch is turned to "RUN," the DRL Control Module will not activate the LO Beam Headlamps until the Park Brake is released.

Battery voltage is applied at all times to the DRL Control Module through the DRL Circuit Breaker or Headlamp/I/P Dimmer Switch to power the LO Beam Headlamps. Voltage is applied to the DRL Control Module through the IGN Fuse and the GAUGES Fuse to power the control circuitry of the DRL Control Module.

As the intensity of light reaching the DRL Ambient Light Sensor decreases, the resistance of the DRL Sensor increases. When the DRL Control Module senses a high resistance (low light conditions) in the DRL Ambient Light Sensor, the DRL Control Module de-energizes the internal DRL Relay and energizes the internal Head Relay. Battery voltage is applied through the closed contacts of the Head Relay to CKT 10. With the Headlamp Dimmer Switch in "LO," the LO Beam Headlamps are "ON" at full intensity. With the Headlamp Dimmer Switch in "HI," the HI Beam Headlamps and Indicator are "ON."

As the intensity of light reaching the DRL Ambient Light Sensor increases, the resistance of the DRL Ambient Light Sensor decreases. When the DRL Control Module senses a low resistance (daylight conditions) in the DRL Ambient Light Sensor, the DRL Control Module de-energizes the internal Head Relay and energizes the internal DRL Relay. Battery voltage is applied through the closed contacts of the Did Relay to the DRL Diode. Due to the voltage drop across the DRL Diode, the LO Beam Headlamps are "ON" at a reduced intensity.

When the Park Brake Switch is closed, CKT 1830 is grounded. If the Ignition Switch is turned to "RUN" when CKT 1830 is grounded, the DRL Control Module senses a voltage drop at the Park Brake Input and will not energize the DRL Relay until the ground through CKT 1830 is removed (Park Brake Switch open).