Table of contents: Hydraulic modulator ↓ Electronic control device ↓ Relay ↓ Wheel speed sensors ↓ Wheel speed sensor rotors ↓
Note: After performing any of the procedures described in this chapter, it is recommended that you have the anti-lock brake system completely checked by your Audi dealer.
Hydraulic modulator
1. Disconnect the negative battery cable.
2. Where equipped, remove the coolant expansion tank as described in Section 2, and move it to the side.
3. Accurately mark the location of each brake line on the hydraulic modulator.
4. Unscrew the cap of the additional brake system reservoir. Cover it with a piece of polyethylene to reduce fluid loss. Alternatively, the fluid can be pumped out of the reservoir into a container.
5. Loosen the union nuts, disconnect the brake lines. Seal the ends of the tubes or cover them with adhesive tape to prevent dust and dirt from entering.
6. Lift the cover off the modulator, disconnect the harness retainer and wiring.
7. Unscrew the mounting nuts and remove the modulator from the suspension.
8. Installation is carried out in the reverse order. Bleed the entire hydraulic system as described in Chapter 17.
Electronic control device
9. It is located under the left rear seat cushion.
10. Check that the ignition is off.
11. Remove the seat cushion (Section 11).
12. Press the locking spring, disconnect the multi-pin plug of the electrical wiring.
13. Unscrew both mounting screws and remove the electronic control device.
14. Installation is carried out in the reverse order, but make sure that the locking spring is fully inserted to secure the multi-pin plug.
Relay
15. There are two relays on the hydraulic modulator, one for the solenoid valve and one for the return pump. There is also a combination relay located in the auxiliary relay box under the instrument panel.
16. Turn off the ignition before removing the relay.
17. First remove the cover, then remove the relay from the socket.
18. To remove the relay from the auxiliary relay block, follow the instructions Section 12.
19. Installation is carried out in reverse order.
Wheel speed sensors
20. Jack up the front or rear of the car and support it on axle stands. Remove the wheel.
21. On early models, the sensor is attached with a bolt. If the sensor is to be reused, mark the exact position of the bolt in the elongated hole with a dab of paint. Remove the bolt, remove the sensor from the bushing in the wheel bearing housing or rear axle. Remove the seal.
22. On later models, the sensor is attached by a clamp sleeve. Pull the sensor out, then remove the clamp sleeve from the wheel bearing housing or rear axle.
23. Release the sensor wiring from the suspension by pulling on the rubber sealing ring.
24. Disconnect the wiring harness connector located in the engine compartment or under the rear seat cushion. On fuel injected models, first disconnect the air duct from the air flow meter and move it to the side.
25. Before installing the rear sensor, check and, if necessary, adjust the rear wheel bearing clearance as described in Section 10.
26. To install the sensor on early models, it is recommended to install a new PVC tip on the sensor. However, if the sensor is to be installed exactly in the marked position, this is not necessary. Install a new seal, coat the seal and sensor with paste. Insert the sensor, tighten the bolt, pressing on the sensor so that the PVC tip touches the rotor.
27. When installing the sensor on later models, first coat the clamp sleeve with paste and insert it completely into the wheel bearing housing or rear axle. Push the sensor completely into the clamp sleeve. Install the rubber boot on the rear sensor (if any).
28. Connect the electrical wiring and, where equipped, the air duct.
29. Insert the rubber sealing ring into the hanger to secure the wiring.
30. Install the wheel and lower the car to the ground.
Wheel speed sensor rotors
31. The front sensor rotors are incorporated into the outer drive shaft joints. The joints can be replaced separately as described in Section 8.
32. Before removing the rear sensor rotor, first remove the hub as described in Section 10.
33. Clamp the hub in a vice and use a punch to knock out the rotor through the holes for the wheel bolt.
34. To install the rotor on the hub, it is necessary to use a metal pipe, being careful not to damage the special sensor.
35. Install the hub as described in Section 10.
[The original article is available on the website «AUDImanual»]