ABS Description and Operation: Notes

The antilock brake system (ABS) consists of the following:

• Antilock brake system (ABS)
• Dynamic rear proportioning
• Hill start assist
• Traction control system
• Vehicle stability enhancement system (VSES)

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 energized when the ignition is ON and no ABS DTCs are present. It supplies battery positive voltage to the solenoid valves and pump motor.
  • Brake pressure sensors - The EBCM contains 2 brake pressure sensors that monitor applied master cylinder pressure to the wheels. The EBCM uses the brake pressure inputs to enhance VSES.
  • Vent tube - The vent tube, located in the EBCM connector, is an opening to the internal cavity of the EBCM. It allows ventilation of the EBCM internals.
• The brake pressure modulator valve contains the hydraulic valves and pump motor that are controlled electrically by the EBCM. The brake pressure modulator valve uses a 4 circuit configuration with a diagonal split. The brake pressure modulator valve directs fluid from the reservoir of the master cylinder to the left front and right rear wheels and fluid from the other reservoir to the right front and left rear wheels. The diagonal circuits are hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on the other.
NOTE: There is a rubber isolator located under the brake pressure modulator valve and on the mounting studs. The rubber isolators protect the brake pressure modulator valve and the EBCM from vehicle vibrations.
• The brake pressure modulator valve contains the following components:
  • Pump motor
  • Inlet valves (one per wheel)
  • Outlet valves (one per wheel)
  • Master cylinder isolation valves (one per drive wheel)
  • Prime valves (one per drive wheel)
  • A master cylinder pressure sensor
• The EBCM sends a 12V reference voltage signal to each wheel speed sensor. As the wheel spins, the wheel speed sensor produces a square wave DC signal voltage. The wheel speed sensor increases the signal frequency as the wheel speed increases, but does not increase the signal amplitude.
• Traction control switch is manually disabled or enabled using the traction control switch.
• Brake pedal position sensor - The EBCM receives a serial data message from the body control module (BCM) to indicate that the brake pedal is applied.
• Yaw rate sensor - The EBCM uses the yaw rate sensor to determine the rate of rotation along the vehicles vertical axis. The yaw rate sensor is packaged with the lateral accelerometer as a single component.
• Lateral accelerometer - The EBCM uses the lateral accelerometer to determine the sideways acceleration of the vehicle. The lateral accelerometer is packaged with the yaw rate sensor as a single component.
• The EBCM uses the power steering control module to determine the position and rotation of the steering wheel.