Description & Operation

CAUTION: See ANTI-LOCK BRAKE SAFETY PRECAUTIONS article in GENERAL INFORMATION.

NOTE: For more information on brake system, see DISC & DRUM - EXCEPT PICKUP & MIATA article.

The Anti-Lock Brake System Control Module (ABS CM) senses reductions in front and rear wheel speed and modulates hydraulic pressure to the brakes to prevent wheel lock-up. The ABS consists of a hydraulic unit, 4 wheel speed sensors and sensor rotors, pump motor and ABS CM. See Fig 1 . An ABS warning light is located on instrument cluster.

Under normal driving conditions, Anti-Lock Brake System (ABS) functions like a standard brake system. When vehicle speed reaches 3.8 MPH, ABS will diagnose pump motor by briefly operating motor. Pump motor operation may be audible inside vehicle.

NOTE: ABS CM is also referred to as an ABS/TCS CM.

ABS CM controls ABS by detecting speed sensor signals and activating solenoid valves in hydraulic unit. ABS CM also controls pump motor and self-diagnostic function. If a problem is detected in ABS, vehicle braking will function like a conventional brake system. ABS warning light will also illuminate.

With detection of wheel lock-up, short pedal pulsations occurring in rapid succession will be felt in brake pedal and steering wheel. Vehicle body may also vibrate slightly. These conditions are normal. Pedal pulsation will continue until there is no longer a need for anti-lock function or until vehicle is stopped.

Fig 1: Identifying ABS Components

Courtesy of MAZDA MOTORS CORP.