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ABS 5.3 (3-Channel System)





ABS 5.3 (3-Channel System) System Description





ABS operation
The ABS control module receives a signal from the brake-light switch and the AC voltage signals from the four speed sensors. These signals are converted into digital wheel-speed signals independently of each other by two microprocessors. The wheel slip (approximately proportional to the computed vehicle reference speed) is formed from these wheel-speed signals.
If vehicle deceleration and excess slip at a wheel are detected, the pressure-holding phase is initiated, i.e. the inlet valve for the relevant wheel is closed to prevent a further increase in pressure. If in spite of the pressure being held constant the wheel tends to continue to lock up, the pressure in the wheel cylinder is reduced. For this purpose, the outlet valve is opened and the brake fluid is pumped back to the brake master cylinder via the return pump (pressure reduction phase) until the wheel turns again. Then, depending on the control cycle, further appropriate cycles are initiated.
This function and the input signals are continuously monitored. If a fault is detected, the control module switches the ABS function off, switches on the ABS warning light and stores the fault in a non-volatile memory in the control module.
In addition, whenever a journey is begun and a speed of 6 km/h is exceeded, a test program is started. The solenoid valves and the pump motor are electrically actuated and checked. If a fault is detected, the control module switches the ABS function off, the ABS warning light is switched on and the fault is stored.
Refer to Function of the individual components.