ABS Description and Operation: Notes

This vehicle is equipped with a Bosch ABS/SCB/TC/VSC module.

This module provides the following vehicle performance enhancement systems:

• Antilock Brake System (ABS)
• Electric Parking Brake (EBP apply and EPB release (automatic)
• Extended Hill Start Assist (EHSA)
• Regenerative Braking (in conjunction with the Eboost module)
• Electronic Brake Distribution
• Traction Control (TC)
• Vehicle Stability Control (VSC)

The following components are involved in the operation of the above systems:

• Electronic brake control module (EBCM) - The EBCM controls the system functions and detects failures.

  The EBCM contains the following components:

  • System relay - The system relay is internal to the EBCM. The system relay is energized when the power button is placed in ON/RUN or a remote function actuation (RFA) commands remote START. The system relay supplies battery positive voltage to the valve solenoids and to the ABS pump motor. This voltage is referred to as system voltage.
  • Solenoids - The solenoids are commanded ON and OFF by the EBCM to operate the appropriate valves in the brake pressure modulator valve.
• Brake pressure modulator valve - The brake pressure modulator valve uses a 4-circuit configuration to control hydraulic pressure to each wheel independently.

  The brake pressure modulator valve contains the following components:

  • ABS pump motor and pump
  • Isolation valves
  • Dump valves
  • Electronic hydraulic control unit
• Steering angle sensor--The EBCM receives serial data message inputs from the steering angle sensor. The steering angle sensor signal is used to calculate the desired yaw rate. The steering angle sensor is mounted internally to the electric power steering gear.
• Traction control switch--Traction control and stability control are manually disabled or enabled by pressing the traction control switch.
• Multi-axis acceleration sensor--The yaw rate, lateral acceleration and longitudinal acceleration sensors are combined into one multi-axis acceleration sensor. The EBCM receives serial data message inputs from the yaw rate, lateral acceleration and longitudinal acceleration sensor and activates stability control depending on multi-axis acceleration sensor input.

  Depending on vehicle options, the vehicle multi-axis sensor may be installed internal to the inflatable restraint sensing diagnostic module, separately externally or a combination of both. Confirm with vehicle RPO codes and schematics.

• Wheel speed sensors - The wheel speeds are detected by active wheel speed sensors and encoder rings. The encoder ring consists of permanent magnets. Each wheel speed sensor receives ignition voltage from the electronic brake control module (EBCM) and provides a DC square wave signal back to the module. As the wheel spins, the EBCM uses the frequency of the square wave signal to calculate the wheel speed.
• Electronic park brake motors - Controlled by the EBCM and attached to each rear caliper.