AUDI A4 1999 B5 / 1.G ABS Bosch 5.0 Workshop Manual

45-6


Anti-lock Brake System (ABS),
Bosch 5.0

CAUTION!

The anti-lock brake system is basically
maintenance-free.
Specialist knowledge is required for
performing any work on this system.
Failure to observe the instructions presented
in this Repair Manual may result in damage
to the system and to loss of vehicle safety.
Pa
ge 1 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
11/19/2002 htt
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45-7


ABS hydraulic unit and brake lines

The tightening torque for all brake lines on the Audi
A4 is 15 Nm (11 ft lb).
1 -
Brake master cylinder with brake servo
unit
Brake master cylinder is shown without
brake fluid reservoir
2 -
Brake line Brake master cylinder/secondary piston
circuit to hydraulic unit Bolted connection at brake master cylinder:
M12x1 Bolted connection at ABS hydraulic unit:
M12x1
3 -
Brake line Brake master cylinder/primary piston circuit
to hydraulic unit Bolted connection at brake master cylinder:
M12x1 Bolted connection at ABS hydraulic unit:
M12x1
Pa
ge 2 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
11/19/2002 htt
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45-8


4 -
Rubber grommet
5 -
ABS wiring harness connector
Release and removeThe connector is part of the ABS wiring
harness. Be aware of different versions for
FWD and AWD models Make sure connector is in the correct
position and properly locked
6 -
Screw 5 Nm (44 in lb)
7 -
Cover panel
8 -
ABS solenoid valve relay
9 -
ABS return flow pump relay
Pa
ge 3 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
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45-9


CAUTION!
Apart from replacing the two relays, repair work
on the ABS hydraulic unit is not permitted. Do
not loosen bolted connections. 10 -
ABS hydraulic unit
Be aware of different versions:
ABS FWD modelsABS/EDL FWD models, ABS/EDL/ASR
FWD models Fig. 1

ABS/EDL AWD models 05.95 Fig. 2ABS/EDL AWD models 05.95 Fig. 3Replace complete ABS hydraulic unit, if
necessary. The ABS hydraulic unit is supplied as a
replacement part that is pre-bled.
Pa
ge 4 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
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45-10


Removing and installing:
- Disconnect battery Ground (GND) strap.
- Seal brake lines and connections
immediately with dummy plugs.
- Bolt new hydraulic control unit to bracket,
item 13 . Remove dummy plugs from
brake line connections. Brake lines
should be connected in accordance with
designations on hydraulic control unit.
Brake line tightening torque: 15 Nm (11 ft
lb)
- Bleed brake system page 47
-23
.
- Carry out high- and low-pressure test
page 45
-5 .
- Carry out On board Diagnostic (OBD)
Repair Manual, ABS/EDL/ASR On Board
Diagnostic (OBD), Repair Group 01. 11 -
Screw
15 Nm (11 ft lb)
Pa
ge 5 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
11/19/2002 htt
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45-11


12 -
Washer
13 -
Bracket for ABS hydraulic unit
Removing and installing page 45
-15
14 -
Bolt and washer assembly
8 Nm (71 in lb)
15 -
Serrated washer
16 -
Ground (GND) cable Ensure good contact
17 -
Hex nut 10 Nm (7 ft lb)
18 -
Brake line ABS hydraulic unit to right-front brake
caliper
19 -
Brake line ABS hydraulic unit to left-front brake caliper
20 -
Brake line ABS hydraulic unit to right-rear brake
caliper
21 -
Brake line ABS hydraulic unit to left-rear brake caliper
Pa
ge 6 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
11/19/2002 htt
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45-12


Brake line connections: 15 Nm (11 ft lb)
Note: Fig. 1 Brake line connections at the hydraulic unit for ABS/EDL,
front wheel drive and ABS/EDL/ASR front wheel drive
1 - Hydraulic unit to brake master cylinder (primary piston circuit)
2 - Hydraulic unit to right-rear brake caliper
3 - Hydraulic unit to left-front brake caliper
4 - Hydraulic unit to brake master cylinder (secondary piston circuit)
5 - Hydraulic unit to left-rear brake caliper
6 - Hydraulic unit to right-front brake caliper
Pressure dampers are not installed on models with all wheel drive and
EDL suction control (from 05.95) Fig. 2
.
EDL suction control minimizes control noises.The working range of the pressure limiting valve in the hydraulic unit is
raised from 90 25 bar (1323 368 psi) to 170 25 bar (2499
368 psi).
Pa
ge 7 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
11/19/2002 htt
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45-13


FIg. 2 Brake line connections at the hydraulic unit, all wheel drive
and ABS/EDL pressure control ( 05.95)
Two pressure dampers are threaded into the hydraulic unit
(arrows) on models with all wheel drive and EDL pressure control
(they smooth out pressure peaks in the brake lines and minimize
control noises).
Counter-hold at the hex on the pressure damper when loosening
the brake line.
1 - Hydraulic unit to brake master cylinder (primary piston circuit)
2 - Hydraulic unit to right-rear brake caliper
3 - Hydraulic unit to left-front brake caliper
4 - Hydraulic unit to brake master cylinder (secondary piston circuit)
5 - Hydraulic unit to left-rear brake caliper
6 - Hydraulic unit to right-front brake caliper
Pa
ge 8 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
11/19/2002 htt
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play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU03.45.2

45-14


EDL suction control was introduced on models with all wheel drive from
05.95. This system reduces the control noises during an EDL control
cycle.
The pressure dampers threaded into the hydraulic unit ( Fig. 2
arrows)
previously used to reduce working noises have been discontinued. The
working range of the pressure limiting valve in the hydraulic unit is raised
from 90 25 bar (1323 368 psi) to 170 25 bar (2499 368 psi).
Connector coding eliminates the risk of incorrectly connecting the
hydraulic unit. Fig. 3 Brake line connections at the hydraulic unit for ABS/EDL,
all-wheel-drive models, suction control (05.95 )
1 - Brake line tightening torque: 15 Nm (11 ft lb)
Pressure damper discontinued. The brake line is now the same
length as for FWD.
4 - Brake line tightening torque: 15 Nm (11 ft lb)
Pressure damper discontinued. The brake line is now the same
length as for FWD.
Pa
ge 9 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
11/19/2002 htt
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yp
e=re
pair&id=AUDI.B5.SU03.45.2

45-15


ABS hydraulic unit mounting bracket,
removing and installing

1 -
Angle bracket
2 -
Bearing bushing
3 -
Buffer
4 -
Mounting bracket for ABS hydraulic unit
5 -
Washer
6 -
Bolt and washer assembly
10 Nm (7 ft lb)
Pa
ge 10 of 12 Anti-lock Brake S
ystem
(ABS
), Bosch 5.0
11/19/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU03.45.2