1993 Audi 90 Quattro Brake Service (ONLINE REPAIR MANUALS)

Audio Coded Anti-Theft System

Some models are equipped with an audio anti-theft system that will disable the audio unit when battery power is interrupted, unless the system is reset the audio unit will not operate.

It is recommended that the anti-theft system code be obtained before attempting any repair that requires battery disconnect. If a code is unavailable, a "Computer Memory Saver" should be plugged into the cigarette lighter to maintain a constant voltage to the audio unit.

If audio unit is disabled proceed as follows to reactivate system.

• Obtain audio unit security code from vehi...

Overhaul

Refer to Fig. when servicing front disc brake calipers, noting the following:

• On A4, A6, Cabriolet, S4, S6, 90 and 100 models, remove piston from caliper housing using replacement tool No. 3272, or equivalent, Fig. .
• On V8 Quattro models, remove piston from caliper housing using replacement tool No. 3272, or equivalent.
• Remove caliper piston seal using a suitable screwdriver, Fig. .
• Install piston as follows:
• Install protective cap with sealing lip onto piston, Fig. .
• Using a suitable screwdriver insert inner sealing lip of protective c...

Brake Pressure Regulator

90

For the following procedure, the vehicle must be empty and standing level on all four wheels, fuel tank must be full and jack and spare tire must be in normal locations.

• Raise and support vehicle using a suitable wheel type lift.
• Ensure vehicle is level and suspension is in normal position.
• Loosen brake compensator spring adjustment bolt and nut.
• Insert pins of adjustment tool No. 3284 into holes on arm and body of brake compensator Fig. .
• Tighten spring adjustment bolt and nut, then remove tool.
• Check brake system pressures as outlined under " Diagnosis ... "

Overhaul

Refer to Figs. and , when servicing front disc brake calipers, noting the following:

• Force piston out brake caliper with compressed air, Fig. . Apply air pressure gradually to guard against sudden release of piston. Place a suitable wooden block into recess of brake caliper to prevent damage to piston.
• Remove caliper piston seal using a suitable screwdriver, Fig. .
• Install piston as f...

Power Supply

1994-95

• Check battery for full charge.
• Check that fuses 3, 12 and anti-lock brake power supply relay fuses are satisfactory. The anti-lock brake power supply relay fuse is located on top of the power supply relay.
• Check for continuity between ABS control unit connector terminal 13 and ground, at battery ground cable. Fig. .
• Turn ignition switch to the Off position.
• Check for continuity between ABS control unit connector terminal 10 and ground.
• Check for battery voltage between ABS control unit plug terminals 1 and 10. Approximate battery voltage should be read.
• If ap...

S4 & S6

Remove

• Raise and support vehicle, then remove wheel assemblies.
• If brake pads are to be reused, then mark installed positions for installation reference.
• Secure brake disc on wheel hub with a wheel lug nut.
• Remove outer brake pad mounting bolts, Fig. .
• Extract part of brake fluid from reservoir using a suitable bleeder bottle, then push piston back into caliper housing by inserting a suitable screwdriver into floating frame and pressing firmly to outside.
• Disconnect wiring harness electrical connector, then remove brake pad wear indicator wiring from bra...