1998 AUDI A4 wheel

01-282
During the test, the individual test steps are
shown in the second line of the VAG1551 scan
tool display. The following abbreviations are
used.
IV = Inlet valve
OV = Outlet valve
LF = Left Front
RF = Right Front
LR = Left Rear
RR = Right Rear
B+ = Battery Positive Voltage (B+) at valve
0V = 0 volts; No voltage at valve
Locked/free = Wheel condition; must be checked
by second technician
Hydr-P = Hydraulic pump
Pa
ge 46 of 64 Basic settin
g (scan tool function 04
)
11/20/2002 htt
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yp
e=re
pair&id=AUDI.B5.SU02.01.15

01-284

Output Diagnostic Test Mode (DTM)
-
ABS hydraulic pump -
V64-

Indicated on display:
ABS hydraulic pump -V64- must start running. This is audible.

When you put your foot on the brake pedal you can feel it vibrating. The
brake pedal vibrates because the hydraulic pump generates pressure
pulses in the brake lines. The pressure pulses generate oscillations.
These are directed to the brake pedal and make it vibrate.
The pressure pulses in the brake lines are not sufficient to lock the
wheels.
Pa
ge 48 of 64 Basic settin
g (scan tool function 04
)
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yp
e=re
pair&id=AUDI.B5.SU02.01.15

01-286

Output Diagnostic Test Mode (DTM)
-
Operate brake

Indicated on display:
-
Press button.
Output Diagnostic Test Mode (DTM)
-
Ifl: 0V
Ofl: 0V
fl wheel locked

Indicated on display:

When you press the brake pedal, brake fluid pressure will be built up in all
four calipers. All four wheels lock.
Requirement for this: mechanical/hydraulic components of the brake
system must be fully functional. This means that the master brake cylinder
is able to build up pressure in all wheel cylinders and the hydraulic
connections and lines are all sealed properly.
Pa
ge 50 of 64 Basic settin
g (scan tool function 04
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.15

01-287


If the wheels do not lock, visually inspect brake fluid reservoir, master
brake cylinder, hydraulic unit, and calipers.
Concentrate on the left-front wheel first. The function of the control
elements for this wheel is tested first.
Note:
This test step in the output diagnostic test mode corresponds to the
"pressure build-up" phase during ABS-controlled braking.
-
Press button.
Pa
ge 51 of 64 Basic settin
g (scan tool function 04
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.15

01-288

Output Diagnostic Test Mode (DTM)
-
Ifl: B+
Ofl: 0V
fl wheel locked

Indicated on display:
- Keep pressing brake pedal.

Inlet valve is activated. It interrupts the brake line. However, fluid pressure
is still maintained in the wheel cylinder. The left-front wheel remains
locked.
Note:
This test step in the output diagnostic test mode corresponds to the
"maintain pressure" phase during ABS-controlled braking.
-
Press button.
Pa
ge 52 of 64 Basic settin
g (scan tool function 04
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.15

01-289

Output Diagnostic Test Mode (DTM)
-
Ifl: B+
Ofl: B+
fl wheel free

Indicated on display:

Keep pressing brake pedal. The inlet valve and the outlet valve for the
left-front wheel are activated. The hydraulic pump starts running and
reduces the fluid pressure in the caliper via the open outlet valve.
The brake pedal must not give, and should press harder against your
foot.
You should now be able to turn the left-front wheel.
Pa
ge 53 of 64 Basic settin
g (scan tool function 04
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.15

01-290
If you cannot turn the wheel, check whether the
brake line for the left-front wheels is connected
correctly.

If yes, this indicates a mechanical malfunction in one of the valves,
providing there is no electrical malfunction in the system. Replace
hydraulic control unit.
If the pedal gives under your foot, this means that the inlet valve or the
check valve activated in parallel to the inlet valve is leaking. Replace
hydraulic unit.
Note:
This test step in the output diagnostic test mode corresponds to the
"pressure reduction" phase during ABS-controlled braking.
-
Press button.
Pa
ge 54 of 64 Basic settin
g (scan tool function 04
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.15

01-291

Output Diagnostic Test Mode (DTM)
-
Ifl: B+
Ofl: 0V
fl wheel free

Indicated on display:
ABS hydraulic pump -V64- will stop running.
- Keep pressing brake pedal. Only the inlet valve is still activated and
interrupts the brake line. If the inlet valve is not leaking, you should be
able to turn the left-front wheel.

If you cannot turn the wheel, this means that the inlet valve or the check
valve activated in parallel to the inlet valve is leaking. Replace hydraulic
control unit.
-
Press button.
Pa
ge 55 of 64 Basic settin
g (scan tool function 04
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.15