The ABS electronic anti-lock braking system regulates the braking pressure transmitted to the wheels, preventing them from losing grip whatever the tyre and road conditions.The system is designed to be incorporated with the braking system (using the same hydraulic fluid) without preventing the operation of the actual braking system if the ABS fails.On the most extensive version the ABS control unit also implements the VDC (Vehicle Dynamic Control), ASR (Anti-Slip Regulation) / MSR (Motor Slip Regulation) functions plus the HBA (Hydraulic Brake Assist) and HH (Hill Holder) functions.The VDC system intervenes on the engine and on the brakes producing a stabilizing torque when the ABS sensors detect conditions that could lead to the vehicle slipping.The VDC system components, in addition to those of the ABS system are:- a sensor that detects the position of the steering wheel (steering angle);- a sensor that detects the rotation of the vehicle around the vertical axis and lateral acceleration (centrifugal force) (yaw sensor);- if the Hill Holder function is present, a longitudinal acceleration sensor is incorporated in the lateral acceleration and yaw sensor;- a sensor which detects the pressure in the ABS hydraulic unit (integrated in the ABS control unit).The VDC system is always combined with the ASR system.The ASR system increases the active safety and stability of the vehicle controlling the slipping of the drive wheels: if slip is caused by the transmission of excessive power, the system cuts in, with the co-operation of the engine management control unit, to reduce engine power output MSR); if, on the other hand, slip is detected at one wheel only, the system cuts in to brake only the slipping wheel by means of the wheel''s modulating solenoid valve.The ASR comes on automatically whenever the engine is started: the system can be deactivated by means of an "ASR VDC" button on the control panel.When the system is off, a led on the button and a warning light on the control panel come on simultaneously. The VDC function, on the other hand, is switched on automatically each time the engine is started up and cannot be turned off.The Hill Holder system is designed to assist the driver when setting off on an incline.In effect the HH is capable of automatically providing sufficient braking torque to keep the vehicle stationary until the clutch is fully released and the engine toruqe is sufficient to start the vehicle comfortably.The HH is automatically activated when the brake pedal is pressed in conjunction with the following conditions: the vehicle speed equal to zero, the gradient more than 2% and the clutch pedal pressed; the moment the brake pedal is released, with all the other conditions being equal, the Hill Holder keeps the braking system pressurized for 1.5 seconds to allow the driver to move their foot from the brake pedal to the accelerator pedal without the vehicle slipping backwards and without using the parking brake.Once the accelerator is pressed, the Hill Holder continues to keep the vehicle still for a further 15 seconds or until the engine torque is sufficient to start the vehicle.The H.B.A. system aids the driver in emergency braking situations when the brake pedal is activated quickly and in poor load maintenance conditions; the system intervenes when the pressure gradient exceeds a certain level (fast application of brake pedal - emergency braking) multiplying the braking pressure at the wheels applied by the driver thereby producing the maximum deceleration that can be achieved.The control unit is equipped with an autodiagnostic function: when an error in the ABS function is detected, the warning light comes on and, at the same time, the system is deactivated; in these conditions the vehicle brakes using the traditional system only.When the control unit detects an error which also affects the EBD function, it turns on the "ABS failure" warning light and the "low brake fluid and handbrake" warning light.Similarly, for the VDC function: the ASR/VDC warning light: the warning light flashes when the system cuts in to notifiy the driver that the ASR has come on due to road grip conditions.When the control unit detects an error in the ASR or VDC function, it turns on the warning light in fixed mode.Lastly, when the control unit detects an error in the HH function, it sends a special message to the instrument panel display.As far as the ABS function only is concerned, See E7020 ABS For more detailsSee descriptions 3350