Daytime Running Lamp: Description and Operation

The daytime running lamp (DRL) system consists of a DRL module and a DRL sensor. Two relays, a DRL relay and a HEAD relay, are integral to the DRL module. The system is designed to automatically operate certain exterior lamps, depending on outside light conditions, whenever the ignition switch is in the RUN position. The system operates in both a DAY arid a NIGHT mode In the DAY mode, the turn signal lamps are lit at full brilliance. In the DAY mode and turn signal switch on, the turn signal lamp will flash normally. In the NIGHT mode, the headlamps are lit at full brilliance along with the front park/turn signal/side marker lamps, and the taillamps.

DAY and NIGHT modes are determined by the signal from the DRL sensor. The DRL sensor is a photosensitive element - a variable resistor that reacts to changes in light intensity. The DRL module monitors the signal from the DRL sensor and determines whether the system should operate in the DAY or NIGHT mode.

When the DRL module is in the DAY mode, the DRL relay is pulled closed and voltage is applied through the module to the turn signal lamps. At nightfall, as light intensity decreases, the DRL sensor signal changes. In response to this change, the DRL module will change from DAY to NIGHT mode as a switching point is crossed. When NIGHT mode is initiated, the DRL relay is opened and the HEAD relay, is pulled closed. Under these conditions, the headlamps, parking lamps arid taillamps receive full system voltage and operate at full brilliance.

If the parking brake is applied before the ignition switch is turned from OFF to RUN, DRL operation is canceled. This function allows the driver to start the engine and keep the headlamps or turn signal lamps OFF-as long as the parking brake is engaged. DRL system operation resumes as soon as the parking brake is released. This deactivation feature only, functions when the parking brake is applied before the ignition switch is turned to RUN. If the parking brake is applied after the ignition switch is turned to RUN, DRL system operation will not be affected.