HDC Relay

WARNING: This page is about a different car, the 2012 Land Rover Range Rover Sport and 2011 Land Rover Range Rover Sport. However, it is still accessible from the selected car via links, so may be relevant.

The HDC relay is used to illuminate the stoplamps when the brakes are activated:

During HDC operation.
During dynamic application of the parking brake. Refer to PARKING BRAKE .
By the adaptive speed control system. Refer to SPEED CONTROL .

The HDC relay is a non-serviceable, solid state relay on the circuit board of the central junction box (CJB). Operation of the HDC relay is controlled by the ABS module switching the coil to ground.

To operate the stoplamps during HDC or adaptive speed control operation, the anti-lock brake system (ABS) module monitors brake system hydraulic pressure and energizes the HDC relay during active braking. A pressure threshold and time filter prevent the stoplamps from flickering when HDC is braking. During dynamic application of the parking brake, the anti-lock brake system (ABS) module energizes the HDC relay when it receives a stoplamp request message from the parking brake module on the high speed controller area network (CAN) bus.