General information regarding the anti-lock braking system

The brake system with which the ABS works is designed in a diagonal pattern. The braking force is increased by means of a vacuum brake booster. Vehicles with A8S do not have mechanical brake force regulators. The control unit software allows you to adjust the amount of braking force on the rear axle. ABS malfunctions do not affect the performance of the brake system and the enhancement of braking force. The brake system performs its functions even if the ABS fails. In the event of a malfunction of the ABS, a change in the ratio of braking forces on the axles must be taken into account. In the event of an ABS malfunction, which is indicated by the illumination of the corresponding control lamp, premature blocking of the rear wheels occurs when braking!

Location of ABS system components

• 1 - Hydraulic unit and control unit
• 2 - Brake booster

The control unit and the hydraulic unit are combined into a single unit. It is forbidden to disconnect these units from each other. It is also forbidden to disconnect the hydraulic pump from the hydraulic unit.

Repair instructions for the anti-lock braking system

In order to detect malfunctions, before carrying out repair work on the ABS system, it is necessary to carry out "troubleshooting". Troubleshooting is carried out using the tester -VAS 5051-. Disconnect the ground wire from the battery with the ignition off. After completing any work that required depressurization of the brake system, the system must be bled using the -VAS 5234- or -VAG 1869- tool. On the final test drive, make sure that the ABS is activated at least once (feel the brake pedal pulsing). When repairing the anti-lock braking system, special attention must be paid to the requirements for maintaining cleanliness, in no case is it allowed to use petroleum products, such as, for example, plastic oils, greases, etc. Before dismantling, carefully clean the connections and the areas that come into contact with them, and do not use aggressive cleaning agents such as brake cleaner, petrol, thinner or similar substances. Place the removed parts on a clean surface and cover. After disconnecting the control unit from the hydraulic unit, use the transport protection for the valves. If repair of depressurized components is not to be carried out immediately, they should be carefully covered or put away in a place that excludes their contamination. Do not use rags that leave their fibers on the parts. Spare parts should be removed from the packaging just before installation. If the system is depressurized, do not work with compressed air and do not move the vehicle. During painting work, a short-term exposure to a temperature of up to 95°C and a long-term effect on the control unit is allowed (about 2 hours) exposure to temperatures up to 85°C. Do not allow brake fluid to enter the electrical connectors.