Electronic Brake Control Module: Description and Operation
ANTI-LOCK BRAKE MODULEThe ABM is a microprocessor-based device that monitors wheel speeds and controls the antilock functions. The ABM contains two microprocessors that receive identical sensor signals and then independently process the information. The results are then compared to make sure that they agree. Otherwise, the ABM will turn off the antilock and turn on the ABS amber warning indicator.
The primary functions of the ABM are to:
^ detect wheel locking tendencies
^ control fluid pressure modulation to the brakes during antilock stop
^ monitor the system for proper operation
^ manage traction control functions
^ provide communication to the DRBIII while in diagnostic mode
^ store diagnostic information in non-volatile memory
The ABM continuously monitors the speed of each wheel. When a wheel locking tendency is detected, the ABM will command the appropriate valve to modulate brake fluid pressure in its hydraulic unit. Brake pedal position is maintained during an antilock stop by being a closed system. The ABM continues to control pressure in individual hydraulic circuits until a wheel locking tendency is no longer present. The ABM turns on the pump motor during an antilock stop.
The antilock brake system is constantly monitored by the ABM for proper operation. If the ABM detects a system malfunction, it can disable the antilock system and turn on the ABS warning indicator. If the antilock function is disabled, the system will revert to standard base brake system operation.
The ABM inputs include the following:
^ diagnostic communication
^ four wheel speed sensors
^ three power feeds: valve, pump, and microprocessor
^ brake lamp switch
^ traction control switch The ABM outputs include the following:
^ ABS warning indicator actuation
^ 12 volts supply to wheel speed sensors
^ Valve actuation
^ diagnostic communication
^ PCI bus communication
^ traction control lamp illumination