Hill Start Assist

When the vehicle is stopped on an incline greater than approximately a 5% 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 FD-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 message sent by the SOBDM over the FD-CAN informs the ABS module the vehicle is not  parked.
• The stability sensor messages sent by the RCM over the HS-CAN2 enable the ABS module to determine if the vehicle is on an incline greater than 2.86 degrees (approximately a 5% grade).

Once the above conditions have been met, hill start assist automatically engages. Before the driver releases the brake pedal, the ABS module commands the HCU to close the isolation valves which maintains the current brake system pressure, preventing 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).