HDC Relay

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

• During HDC operation.
• During dynamic application of the parking brake.

  For additional information, refer to: PARKING BRAKE .

• By the adaptive speed control system. For additional information, refer to: Speed Control (V8 4.4L Petrol), Speed Control (V8 S/C 4.2L Petrol).

The HDC relay is a non-serviceable, solid state relay on the circuit board of the 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 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 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.