Anti-Lock Brake System (Abs) Module

The Powertrain Control Module (PCM) receives information from the Brake System Module (BSM) over the CAN bus. The PCM uses this information for many reasons including Engine Stop/Start operation.

• Wheel speed sensor data
• Brake pedal position
• Brake system pressure
• Hill Start Assist (HSA) status

For an auto-stop event to occur the PCM must detect vehicle speed at 0 and brake pedal input. The BSM receives the dynamic sensor data from the Occupant Restraint Controller (ORC) to determine if a grade is present and verifies that sufficient brake system hydraulic pressure is present for HSA. One of the following HSA status messages is then sent out on the CAN bus.

• HSA is not active/pending. This indicates that the HSA activation requirements are yet to be determined or the vehicle is not at a stand still.
• Vehicle stand still has been detected and the HSA is not holding braking system pressure.
• A stand still and grade have been detected and the HSA signal is indicating the minimum braking system pressure required to hold the vehicle on the grade. The BSM will quickly transition to the required braking system hydraulic pressure after determining vehicle stand still and detection of the grade. The minimum braking system pressure signal can differ from the actual pressure that the brake system is holding. The PCM will compare the brake master cylinder pressure to the signal to ensure that enough brake system pressure is present to hold the vehicle before an ESS auto-stop event is performed.

The HSA feature helps prevent rollback on an uphill grade, or the vehicle lurching forward when the engine starts on a downhill grade. The HSA feature is controlled by the BSM software. The HSA feature will hold the brake system hydraulic pressure until the engine has started and accelerator pedal input is detected. These inputs are communicated to the BSM over the CAN bus from the PCM. Once these inputs are detected the BSM will quickly ramp out brake system pressure.

The HSA feature will continue to function for ESS even when the HSA feature is disabled by the customer using the programmable options menu to turn the HSA system off.