Daytime Running Lamp: Description and Operation

DAYTIME RUNNING LAMPS (DRL)

NOTE: The smart junction box (SJB) must be configured when installing a new module. See PROGRAMMABLE MODULE INSTALLATION. Programmable Module Installation

The DRL system operates the low-beam headlamps at a reduced intensity. The SJB supplies pulse width modulated (PWM) voltage to the low-beam headlamps when the following conditions are met:
- The high beam headlamps are not on.
- The ignition switch is in the RUN position.
- The parking brake control is released.

The DRL system utilizes the existing circuitry in the vehicle.

DAYTIME RUNNING LAMPS (DRL)

Principles of Operation

NOTE: The smart junction box (SJB) is also known as the generic electronic module (GEM).

The daytime running lamps (DRL) are controlled by the SJB. The SJB operates the low beam headlamps at a reduced intensity. The DRL driver (integral to the SJB) supplies pulse-width modulated (PWM) voltage to the low beam headlamps when the following conditions are met:
- The high beam headlamps are not on.
- The ignition switch is in the RUN position.
- The parking brake is not engaged.

The SJB utilizes a protective circuit strategy for many of its outputs (for example, the headlamp output circuit). Output loads (current level) are monitored for excessive current (typically short circuits) and are shut down (turns off the voltage or ground provided by the module) when a fault is detected. A continuous diagnostic trouble code (DTC) is stored at that time for the fault. The circuit then resets after an ignition cycle or customer demand of the function (switching the component on, battery saver being energized).
When an excessive circuit load occurs several times, the module shuts down the output until a service procedure is carried out. At the same time, the continuous DTC that was stored on the first failure cannot be cleared by a command to clear the continuous DTCs. The module does not allow this code to be cleared or the circuit restored to normal until a successful on-demand self-test proves that the fault has been repaired. After the on-demand self-test has successfully completed (no on-demand DTCs present), the continuous DTC clears and the circuit function returns.