Daytime Running Lamp Control Unit: Description and Operation

The Daytime Running Lamps (DRL) System operates the vehicle Hi Beam Headlamps at reduced power during the daytime to make the vehicle more visible to other drivers.

Voltage is present at the coil and contacts of the Headlamp Relay at all times through the HEAD Fuse Link Cartridge; voltage is also present at the DRL Relay contacts through this same fuse link cartridge. With the Ignition Switch in RUN, voltage is present at the DRL Relay coil and the DRL Module through the REAR WIPER Fuse.

With the Ignition Switch in RUN, the Park Brake fully released, and the Headlamps turned OFF, the DRL Module grounds the DRL Relay coil. The coil is energized and the Relay contacts close. Current flows through the HEAD Fuse Link Cartridge, the DRL Resistor and the Hi Beam Headlamps to ground. The Headlamps illuminate at reduced power. When the DRL System is in operation, the Instrument Cluster Hi Beam Indicator is not illuminated.

Applying the Parking Brake or turning on the Headlamps disables the DRL System. Applying the Parking Brake grounds pin A of the Module. Turning on the Headlamps in the Lo beam position applies 12 volts at pi H of the Module. Turning on the Headlamps in the Hi beam position applies 12 volts at pin J of the Module. The diode shown inside the DRL Module prevents low brake fluid level from disabling the DRL System.

During regular Hi Beam Headlamp operation, the DRL Module outputs 12 volts at pin l to illuminate the Hi Beam indicator.

On 1.8L engine equipped vehicles, a "DRL ON" signal is supplied to the EGI Control Module when the DRL System is operating.