Daytime Running Lamp: Description and Operation

The ambient light sensor is a light sensitive transistor that varies its voltage signal to the Body Control Module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal it will either turn on the Daytime Running Lamps (DRL) or the headlights for auto headlamp operation. Any function or condition that turns on the headlights will cancel the daytime running lamps operation. With the headlight switch in the OFF position, the headlights will either be turned ON or OFF, after an approximate 8 second delay depending on whether daylight or low light conditions are sensed. The DRL will operate when the ignition switch is in the RUN position, the gear selector is not in the PARK position and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.

DRL operation in Manual Transmission equipped vehicles will occur when the ignition switch is in the RUN position, and the parking brake is released. The Automatic Lamp Control (ALC) system and the daytime running lamps (DRL) feature, except the Canadian version, can be temporarily disabled by performing the following procedure:
1. Turn the ignition to RUN.
2. Press the DOME OVERRIDE button 4 times within 6 seconds.

A chime will sound informing you that the system is off. The system will remain disabled until the ignition is cycled off and then on or by pressing the DOME OVERRIDE button 4 more times within 6 seconds. The chime will sound again signaling that the system has been reactivated.

All-Except ZR2
The DRL relay is supplied battery positive voltage by the FOG LP fuse in the underhood fuse block. When the BCM requests DRL operation, the DRL relay coil and headlamp grounding relay coil are grounded by the BCM activating both relays. The energized headlamp grounding relay removes the ground utilized in normal headlamp operation to the multifunction headlamp dimmer switch. The energized DRL relay reroutes the LH high beam supply voltage circuit to ground at G102. These actions result in the LH and RH high beam headlamps to function in a series circuit at a reduced intensity.

On some vehicles, the DRL will turn OFF when the turn signal lamps are activated. This is controlled by the BCM and is a normal condition.

ZR2
On a vehicle with the ZR2 option, the daytime running lamps utilize the low beam headlamps equipped with a long life bulb in a parallel circuit. Voltage is supplied by the headlamp power relay as in normal low beam operation to each low beam headlamp bulb however the ground is controlled by the DRL relay.

When the BCM requests for DRL operation, it will apply battery positive voltage energizing the headlamp power relay coil and ground activating the DRL relay coil. The DRL relay bypasses the multifunction headlamp dimmer switch completing the headlamp low beam ground circuit to G102. The parameters required to operate the system are the same as a vehicle without the ZR2 option.

For a description of the RPO Code(s) shown in this article or any of the images therein, refer to the RPO Code List found at Vehicle/Application. Application and ID