Hill Start Assist

When the vehicle is stopped on an incline greater than 1.5 degrees (approximately a 3% grade), the ABS  module holds the brake pressure for approximately 1.5 seconds while the driver transitions from the brake pedal to the accelerator pedal. This is accomplished by monitoring several HS-CAN  messages and several sensors to determine if the vehicle is stopped and not parked, and if the vehicle is on an appropriate incline. The brake pedal message sent from the PCM  over the HS-CAN  and the wheel speed sensor inputs allow the ABS  module to determine the vehicle has come to a complete stop. The transmission selector lever messages sent by the PCM  informs the ABS  module the vehicle is not parked. The stability sensor messages sent by the RCM  over the private HS-CAN  enable the ABS  module to determine if the vehicle is on an incline greater than 1.5 degrees (approximately a 3% grade). Once the above conditions have been met, the hill start assist function automatically engages. As the driver releases the brake pedal, the ABS  module commands the HCU  to close the isolation valves to maintain the current brake system pressure and prevent the vehicle from rolling down the incline. Once the driver presses the accelerator pedal and the engine RPM increases, the ABS  module gradually releases the brake pressure to make sure the vehicle is neither rolling back nor driving off until there is sufficient driving torque to accelerate the vehicle forward (or backward if reversing up the incline).