The electronic anti-lock brake system (BOSCH
5.3 ABS) governs braking pressure sent to the wheels and prevents
loss of grip under all tyre and road surface conditions. The system is designed to complement the
normal mechanical braking system and not to replace it. In this
way it ensures effective safety in the case of anomalies: the ABS
uses the same fluid as the conventional mechanical braking system.Four sensors fitted to the four wheels inform
the electronic control unit of wheel speed at every moment. In this
way, they detect wheel lock, wheel slip and loss of grip. Under these conditions, the control unit
sends specific instructions to solenoids that modulate hydraulic
circuit pressure to eliminate lock and restore the car to within
grip limits. This ensures the shortest possible stopping distance,
without losing control of the steering.Two adjustment solenoids (one for pressure
charging, the other for pressure discharging) are fitted for each
wheel.The sensors are active, i.e. they consist
of a Hall-effect receiver that faces a magnetic coding device built
into the hub bearing. Under these conditions, the signal is less
influenced by electromagnetic interference and temperature.The control unit also controls brake force
distribution over the rear axle and thus replaces the mechanical
load proportioning valve used previously (EBD function: Electronic Brake
Distribution).The control unit is equipped with a self-diagnostic
function: when an error occurs in the ABS system, a warning light
is turned on and the system is simultaneously deactivated. Under
these conditions, the car brakes using only the conventional system.When the control unit detects an error in
the EBD function, it simultaneously turns on the 'insufficient brake
fluid level' and 'handbrake on' warning light as well as the ABS warning
light.Under these conditions, the rear brake distribution
control is also deactivated and the car must be driven with great
care.
For more details
see DESCRIPTION AND OPERATION: 3340 A(B.S. ANTI-LOCK BRAKING
SYSTEM .)The supply lines for the control unit and
the various system components (sensors and actuators) are protected
by a special maxifuse, located near the control unit, and by a fuse in
the engine compartment in the relay and fuse box.