Hill Descent Control (HDC) Signal

Hill Descent Control (HDC) Signal
The ECM transmits throttle angle, engine torque, engine identification (Td5 or V8), and transmission type (automatic or manual) data to the SLABS ECU to support the Hill Descent Control system. The information is transmitted via a - 12 V pulse width modulated (PWM) signal at a frequency of 179.27 Hz.

Function
The HDC signal output from the ECM is via pin 29 of connector C0636. The ECM generates a PWM signal that varies in pulse width in accordance with changing throttle angle or engine torque. The throttle angle data is transmitted on pulses 1, 3, 5 and 37. The engine torque data is transmitted on pulses 2, 4, 6 and 38. The engine and transmission information is transmitted on pulse 39. A synchronising pulse is transmitted after every 39th pulse.

The HDC signal can fail in the following ways:
^ Harness or connector damage

A HDC signal failure may be evident from the following:
^ HDC/ABS warning light on
^ HDC inoperative
^ Audible warning

Should a malfunction of the HDC signal occur, the following fault codes may be evident and can be retrieved by TestBook: