Daytime Running Lamp Relay: Operation

WARNING: This page is about a different car, the 2005 Jeep Liberty. However, it is still accessible from the selected car via links, so may be relevant.

The Daytime Running Lamps (DRL) relay is a solid state relay that controls the flow of battery current to the high beam filaments of both headlamp bulbs based upon a duty cycle control input received from the Body Control Module (BCM) of vehicles equipped with the DRL feature. By cycling the DRL relay output, the BCM controls the illumination intensity of the high beam filaments. The DRL relay is connected to the vehicle electrical system through a receptacle in the Junction Block (JB). The inputs and outputs of the DRL relay include:

Battery Voltage Input - The DRL relay receives battery voltage on a fused B(+) circuit from a fused B(+) fuse in the Power Distribution Center (PDC).
Ground Input - The DRL relay receives a path to ground through a splice block with an eyelet terminal that is secured by a nut to a ground stud on the driver side instrument panel end bracket near the JB.
Control Input - The DRL relay control input is received from the BCM and/or the momentary optical horn (flash-to-pass) output of the multi-function switch through a high beam relay control circuit.
Control Output - The DRL relay supplies Pulse Width Modulated (PWM) battery voltage to the headlamp high beam filaments through the high beam relay output circuit.

Because of active electronic elements within the DRL relay, it cannot be diagnosed or tested using conventional diagnostic tools and procedures. If the DRL relay is believed to be faulty, test and repair the headlamp system as necessary. If no problem is found in the headlamp system, replace the DRL relay with a known good unit to confirm system operation.

The DRL relay cannot be repaired and, if faulty or damaged, it must be replaced. Refer to SYSTEM WIRING DIAGRAMS for diagnosis and testing of the DRL relay and for complete exterior lighting wiring diagrams.