Audi Workshop Service and Repair Manuals

ESP incorporates the following functions: EBPD, ABS, EDL and ASR. The tasks of the individual components are as follows:

EBPD

The brake system is split diagonally into two hydraulic circuits, one for supplying the front left and rear right brakes and the other for supplying the front right and rear left brakes.

The ABS with EDL control unit -J104 is programmed with specially designed software for electronic brake pressure distribution (EBPD), which takes over the function of the mechanical/hydraulic brake pressure limiter.

In cases where ABS failure has occurred but the electronic brake pressure distribution function can still be maintained by a back-up feature, the signal transmitted to the dash panel insert is pulsed. The dash panel insert distinguishes between three conditions: No signal, pulsed signal and constant signal. The ABS warning lamp and the red "brake system malfunction" symbol light accordingly.

•     1 -    → Terminal 15
•     2 -    Signal for actuation of ABS warning lamp and red "brake system malfunction" symbol
•     3 -    Power supply for ABS warning lamp
•     4 -    Power supply for red "brake system malfunction" symbol

•     A -    In phase "A" (after ignition is switched on), ABS warning lamp is actuated for two seconds during self-test by means of signal "2" and comes on. During this phase, the dash panel insert automatically suppresses lighting of the red "brake system malfunction" symbol. Suppression only takes place if engine speed is < 2000 rpm or vehicle speed is < 20km/h.
•     B -    There is no signal "2" in phase "B". Neither ABS warning lamp nor red "brake system malfunction" symbol come on.
•     C -    In phase "C" self-diagnosis has detected a fault which does not cause EBPD to be deactivated. Signal "2" is pulsed. Only the ABS warning lamp lights.
•     D -    In phase "D" self-diagnosis has detected a fault which causes EBPD to be deactivated. Signal "2" is constantly applied. Both ABS warning lamp and red "brake system malfunction" symbol come on.

Lighting of the red "brake system malfunction" symbol indicates failure of EBPD. Extra caution must be taken if the vehicle has to be driven in this condition , "Test drive".

For further information on actuation of warning lamps in connection with EBPD function, refer to: "Description of warning lamp functions"
=> Page 01-50

ABS:

The ABS prevents locking of the wheels when the brakes are applied by the driver. It regulates the brake pressure applied to the individual wheel brake cylinders as a function of the rate of acceleration/deceleration at the wheels (which depends on the amount of wheel slip) in such a manner that the wheels can develop maximum road adhesion and thus the best possible braking effect.

EDL:

The electronic differential lock (EDL) is designed to provide assistance when driving off. Electronically controlled brake application on the spinning drive wheel provides a torque reaction point for the differential. This enables the wheel with the better traction to make use of the engine power. The EDL is also effective when reversing.

In conjunction with ESP, EDL is active at vehicle speeds of up to 80 km/h.

ASR:

A prerequisite for the ASR function is that the ABS with EDL control unit -J104 can exchange data with the engine control unit and - in the case of vehicles with automatic gearbox - with the gearbox control unit. In other words, the control units must be able to communicate.

Data are transferred by way of the CAN bus => Page 01-30.

By reducing engine power, ASR stops the drive wheels spinning on acceleration. The function can be employed over the entire vehicle speed range. EDL and ASR complement one another when accelerating.

ESP:

ESP stands for Electronic Stability Program. It is designed to stabilise the dynamic handling response of the vehicle by counteracting any tendency towards oversteer or understeer. EBPD, ABS, EDL and ASR functions are incorporated into the system. Its characteristic feature is however controlled brake application at individual wheels.

Examples:

→ In the event of oversteer, the rear of the vehicle breaks away and the vehicle rotates further about its vertical axis than is required for cornering. The system counteracts this excessive movement by applying a controlled braking force at the outside front wheel.

→ In an understeer condition, the front end of the vehicle does not follow the required cornering radius and breaks away. The vehicle does not rotate far enough about its vertical axis to maintain course through the bend. The system increases the amount of rotation by applying a controlled braking force at the inside rear wheel.