Electronic Brake Control Module: Description and Operation

The Electronic Control Unit (ECU), which receives power from the system relay, is a sealed module. No attempt must be made to open it.

The function of the ECU is to process the information (signals) received from the wheel sensors and translate it into control (Pulse Width Modulation (PWM)) signals to the solenoid valves. The ECU monitors most of the electrical components of the Antilock Brake System (ABS) system. It also monitors itself for electronic circuit faults.

If a fault is detected, the ECU will cut out the ABS system and switch on the ABS (Anti-lock) warning light.





The ABS system will be inoperative when the ECU detects a discontinuity in a valve block or wheel sensor circuit. The ignition must be switched off and the fault rectified before the ABS warning light can be extinguished and the ECU started up again. If the fault is rectified without the ignition being switched off, the ABS warning light will remain lit.

A weak signal level from the wheel sensors causes the ABS system to become inoperative and the ABS warning light to come on.

When the ABS system is inoperative, the brake system functions like a conventional brake system with a vacuum assisted servo.

The signals from the wheel sensors are processed by the ECU, which computes a reference speed for the vehicle. The individual signals are then compared with this reference speed. If any of the signals depart from this reference value, the modulating procedure will be activated, as follows:

Phase 1
Lock-up tendency detected. System prevents increase in brake pressure.

Phase 2
Initiation of ABS modulation. Brake pressure reduced, held constant or increased, depending on increase or decrease in wheel rpm.

Phase 3
Tendency for wheel to lock gone. Brake pressure increased depending on road adhesion checked in phase 2.