General description

GENERAL DESCRIPTION

The vehicle is equipped with an electronic system to prevent the wheels of the vehicle from locking (ABS). This system regulates 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 substitute, the normal mechanical braking system, guaranteeing a high degree of safety in the event of a braking anomaly. The intervention is carried out on the same brake fluid found in traditional mechanical circuits. Four sensors located on the four wheels communicate the speed of the wheels to the control unit, showing up locking situations affecting the wheels, skidding and loss of road holding.

In these situations, the control unit actuates solenoid valves which regulate the pressure in the hydraulic circuit, eliminating wheel locking and restoring road-holding which means that braking distance is reduced to a minimum without loss of steering control.

There are only three solenoid regulating valves in this version of the system: one for each of the two front wheels and one common to both the rear wheels which are regulated in parallel by a sequential control valve.

The system is composed of:

• four magnetic induction sensors which measure wheel speed L28; L29, L30, L31.
• an integrated hydraulic/electronic control unit N51, where the following components are located:

• electronic control module
• three solenoid valves
• brake fluid pump
• safety relay
• pump control relay
• self-diagnosis connector T1
• brake switch H3 (the same switch which also lights up the stop lights) which signals the braking state to the system.

The ABS system includes a self-diagnosis system which continually monitors all the components and the operating parameters of the system. In the event of a malfunction or fault the system automatically cuts itself out leaving the traditional servo-assisted braking system operational: this is communicated to the driver by way of the warning lamp located on the Instrument panel.

Connecting up to the diagnosis connector (T1) located near the control unit, it is possible to use the signals of the flash code to rapidly identify the faulty component (see Troubleshooting).

The connector T1 can also be used to connect the ALFA ROMEO Tester system.

The "ABS malfunction" warning lamp also comes on when the vehicle is started and will go out after a few seconds, thus signalling to the driver that the initial system testing has been carried out and no anomaly found.

FUNCTIONAL DESCRIPTION

The key-operated supply powers the coil of the safety relay via pin 1 of connector G272. The safety relay is located inside control unit N51, which supplies the electronic module and the engine relay coil with battery voltage, coming from pin 2 of G272. Following a command from the electronic module, this actuates the pump motor.

The electronic module and the relays are connected to ground via pin 3 of connector G272, while the pump is grounded through connector G202.

Inside the control unit, the module is connected to the three regulating solenoid valves while externally it is connected via connector G273, to the four sensors L28 - L29 - L30 - L31 which signal the speed of the individual wheels, and to the brake switch H3. The consensus signal from the brake switch prevents the system from intervening when the brake pedal is not depressed.

When the control unit detects a problem via the self-diagnosis function, it sends a signal to the instrument panel C10 which then lights up the "ABS malfunction" warning lamp; this signal is dependent upon the malfunctioning of the electronic module -pin 1 of connector G273- or of the hydraulic control - pin 4 of G272.

The diagnosis connector T1, can be used to connect the control unit to the ALFA ROMEO Tester or to permit "reading" of the flashing code (see Troubleshooting).