Supplemental Braking Assist

The ABS module utilizes the HCU  and hydraulic pump motor to aid in bringing the vehicle to a safe, controlled stop in the event of severe vacuum loss at the brake booster. The ABS module continually monitors the vacuum in the brake booster through the use of a vacuum sensor. When the vacuum sensor indicates vacuum is below a predetermined level, a DTC is set in the ABS module. The ABS module sends a message to the IPC  over the HS-CAN  to illuminate the red brake warning indicator. If a low vacuum condition occurs during a braking event or if the driver attempts to stop the vehicle with a low vacuum condition in the brake booster, the ABS module activates the hydraulic pump motor in the HCU  to assist with vehicle braking.

Limousine vehicles also utilize an electrically operated pump to supply additional vacuum to the brake booster. The ABS module controls the pump through the use of a solid state relay, when activated, the relay supplies voltage to the brake vacuum pump. The relay activates the pump based on information received from the brake booster vacuum sensor.

On vehicles equipped with adaptive cruise control, the C-CM monitors the area forward of the vehicle. When an object enters this area and closes the distance gap set by the driver, the C-CM sends a deceleration request to the ABS module over the HS-CAN  (either an adaptive cruise control deceleration request or a collision avoidance deceleration request). When the deceleration request message is received, the ABS module activates the hydraulic pump motor and solenoid valves in the HCU  to slow the vehicle down to maintain the distance gap set by the driver. Once the distance gap set by the driver is achieved, the C-CM stops sending the deceleration request message and the ABS module deactivates the hydraulic pump motor and solenoid valves in the HCU  . If the C-CM determines that the amount of braking provided by the ABS module is insufficient, the C-CM sends a forward collision avoidance braking request message to the ABS module and warns the driver, both audibly and visually, through the use of the HUD  . After receiving the braking request message, the ABS module waits for brake pedal input and at that time applies maximum braking assist using the hydraulic pump motor and the HCU  . For additional information on the adaptive cruise control system, refer to CRUISE CONTROL - ADAPTIVE . For additional information on the collision avoidance system, refer to COLLISION AVOIDANCE .