Daytime Running Lamp Relay: Description and Operation

Daytime Running Lamp Relay:

The Daytime Running Lamp (DRL) relay is a solid state relay that is used only on vehicles manufactured for sale in Canada. The DRL relay is installed in the Junction Block (JB) on the driver side outboard end of the instrument panel. Vehicles equipped with this relay do not have a headlamp high beam relay installed in the JB.

The DRL relay features a die cast aluminum housing that serves to contain the solid state circuitry of the relay as well as to perform as a heat sink. Potting material fills the base of the housing to enclose and protect the circuitry.

Four male spade terminals exit the base of the relay housing through the potting material to connect the relay to the vehicle electrical system. These terminals are laid out in a footprint that is similar to that of a conventional International Standards Organization (ISO) relay; however, a standard ISO relay must never be installed in place of the DRL relay.

The DRL relay cannot be adjusted or repaired and, if faulty or damaged, it must be replaced with a new unit.

The Daytime Running Lamps (DRL) relay is a solid state relay that controls the flow of battery voltage 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 the appropriate wiring information for diagnosis and testing of the DRL relay and for complete exterior lighting wiring diagrams.