Electronic Brake Control Module: Description and Operation

This solid-state component evaluates wheel speed signals, and calculates allowable wheel slip for optimum braking. In order to determine optimum wheel slip precentages the ECU monitors inputs from the wheel speed sensors, brake switch, pump relay, and hydraulic modulator solenoids. After making this calculation, it controls wheel circuit hydraulic pressure. When a wheel sensor signals excessive wheel deceleration (imminent lockup), the ECU first sends a signal that tells the hydraulic modulator to isolate that hydraulic wheel circuit. If excessive wheel deceleration continues, the ECU signals the hydraulic modulator to reduce the hydraulic pressure in that wheel circuit. After reducing pressure, the wheel accelerates; when acceleration reaches a preset level, the ECU signals the hydraulic modulator to increase wheel circuit pressure. This action again causes wheel deceleration, and the control cycle begins over. In addition to being the "brain" of the ABS, the ECU tests and monitors itself and the anti-lock system using a defined program.