General description

GENERAL DESCRIPTION

The car is equipped with an electronic wheel anti-lock system (BOSCH 2Si) which adjusts the braking pressure transmitted to the wheels preventing loss of road-holding under all tyre and road conditions.

The system has been designed to integrate, and not replace, the normal mechanical braking system, guaranteeing a high degree of safety in the event of a failure: in fact it operates on the same brake fluid as the conventional mechanical circuit.

Four sensors, located on the four wheels, inform the electronic control unit of the speed of each wheel continuously, thereby recording locking situations affecting the wheels, skidding and loss of grip.

In these situations, the control unit suitably operates the solenoid valves that modulate the pressure in the hydraulic circuit, eliminating wheel locking and bringing the car back to the limit of roadholding, which means that the braking distance is reduced to a minimum, without losing control of steering.

The modulating solenoid valves are, in this version of the system, four, one for each wheel.

Components

The system comprises:

• four magnetic induction sensors which read the speed of the wheels: L28; L29; L30; L31.
• the integrated electronic and hydraulic control unit N51, which houses the following:
  • the electronic control module (CPU)
  • the four solenoid valves
  • the brake fluid pump
  • a safety relay
  • a pump control relay
• the connector for self-diagnosis T8
• the brake switch H3 (the same that turns on the stop lights) which signals the system the braking condition.

The ABS includes a self-diagnosis system which continually monitors all the system parameters and components: in the event of a failure or fault, the system cuts itself off automatically leaving the conventional servo-assisted mechanical braking system operational: the driver is alerted of this situation by a special warning light [symbol] on the instrument cluster (C10).

FUNCTIONAL DESCRIPTION

System supply:

With a line protected by wander fuse G125a (10A) the key- operated voltage - leading from relay I108 and from fuse G384 - supplies pin 1 of connector G272 of the ABS hydraulic unit N51, and from here it supplies the safety relay and energizes the coil: this way the relay supplies with battery voltage-leading from pin 2 of G272 and from the line protected by fuse G125b (60A) - the electronic module and the coil of the engine relay: following a command from the electronic module, this operates the pump motor which delivers the pressure of the brake fluid to the wheels.

The electronic module and relays are earthed by pin 4 of connector G272, while the pump is earthed by connector G202.

Sensors and solenoid valves:

Directly inside the control unit N51, the module is connected with three adjustment solenoid valves, which modulate the pressure on the brakes of the four wheels; outside, through connector G273, it is connected with the four sensors L28 - L29 - L30 - L31 which signal the speed of the single wheels, and with the brake switch H3, which sends a consent signal: in fact the ABS system cannot come into operation if the brake pedal is not pressed.

Self-diagnosis:

When the control unit detects problems through the self- diagnosis function, it sends a signal to the instrument cluster C10 which turns on the ABS warning light: this signal depends on a failure of the electronic module-pin 1 of connector G273- or on the hydraulic control - pin 3 of G272. The diagnosis connector T8, allows connection of the control unit with the ALFA ROMEO Tester or "reading" of the flashing code (see "Fault-finding").

Connecting to the diagnosis connector (T8) located next to the control unit, it is possible to use the signals of the "flashing code" to quickly locate the faulty component (see "Fault-finding").

The connector T8 can also be used to connect to the ALFA ROMEO Tester.