The electronic antilock braking system (ABS) and wheel slip system regulates the braking pressure transmitted to the wheels, preventing them from losing grip whatever the tyre and road conditions.On the most extensive version the ABS control unit also implements the ESP (Electronic Stability Program) and ASR (Anti-Slip Regulation) functions plus the HBA (Hydraulic Brake Assist) and H.H. (Hill Holder).The ESP 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 ESP system components, in addition to those of the ABS system are:- a sensor that detects the position of the steering wheel (steering angle note);- a sensor that detects the rotation of the vehicle around the vertical axis and lateral acceleration (centrifugal force) and longitudinal acceleration (yaw control unit).- a sensor which detects the pressure in the ABS hydraulic unit (integrated in the ABS control unit).The ESP 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. 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 switched off using the "ASR OFF" button located on the centre tunnel level with the gearbox trim.When the system is off, an LED on the button and the (ESP system failure) warning light in the control panel come on simultaneously.The ESP 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 uphill or downhill.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 with the engine on and when the brake pedal is pressed in conjunction with the following conditions:- uphill, vehicle speed equal to zero, gradient more than 5% and clutch pedal pressed;- downhill, vehicle speed equal to zero, gradient more than 5% and clutch pedal pressed and reverse gear engaged.The moment the brake pedal is released, with all the other conditions being equal, the Hill Holder keeps the braking system pressurized for 2 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 10 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 is detected in the various functions, it manages the different modes for switching on the warning lights in the instrument panel.ASR/ESP 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 ESP function, it turns on the warning light in fixed mode. The warning light comes on constantly even when the Hill Holder system is faulty.ABS warning light: the warning light comes on when the control unit detects an error in the ABS function and simultaneously deactivates the system.Insufficient brake fluid level/handbrake applied warning light: the warning light comes on when the control unit detects an error in the operation of the EBD logic.