Hill Descent Control Signal

Hill Descent Control (HDC) Signal Description

HDC operates in conjunction with the anti-lock braking system to provide greater control in off-road situations if necessary. HDC can be selected with the vehicle in any gear, but will only operate when low range gears are engaged with the vehicle traveling at less than 31 mph.
During a descent, if engine braking is insufficient to control the vehicle speed, HDC (if selected) automatically operates the brakes to slow the vehicle and maintain a speed relative to the selected gear and the accelerator pedal position.

The ECM transmits throttle angle, engine torque, engine identification (V8 Thor) and transmission type to the SLABS control module to support the HDC system. This information is transmitted via a multiplexed PWM waveform.

The ECM has power stage diagnostics for the signal, with a fault being detected if any of the following conditions is satisfied:
1. HDC link to the SLABS control module short circuit to battery positive, i.e. the driver voltage is greater than half the battery voltage when the driver is ON.
2. HDC link to the SLABS control module short circuit to ground, i.e. the driver voltage is less than one third of the battery voltage when the driver is OFF.
3. HDC link to the SLABS control module open circuit, i.e. the driver voltage is greater than one third of the battery voltage but less than two thirds of the battery voltage when the driver is OFF.