1999 AUDI A4 ABS

01-281

Notes:

The vehicle must be raised until all wheels are
free to turn. Ask a colleague to help. The
colleague will have to check the wheels to
determine whether they turn freely.
You can stop the test sequence at any time by
pressing the -C- button.
To avoid overloading the components being
checked, they are actuated during the test
sequence for a period of 60 (or 90) seconds.
The actuator test will be terminated if the "
button" is not pressed within this period.

The ABS warning light and the red "brake
system malfunction" symbol blink during the
test.
Pressing the brake pedal repeatedly this
relieves the vacuum in the brake booster. For
this reason, the brake pedal must be pressed
harder in order to achieve the same braking
effect. Your work will be easier if you run the
engine briefly. This will build up vacuum in the
brake booster again.
Pa
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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
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01-285


The hydraulic circuit diagram shows a systematic representation of
an ABS/EDL system. This will give a better understanding of the
various test steps in the output Diagnostic Test Mode (DTM).
shaded components are in action.Thin solid lines represent hydraulic lines or hoses that are not under
pressure. Thick broken lines represent hydraulic lines or hoses working as
suction lines. Thick solid lines represent hydraulic lines or hoses that are under
pressure.
-
Press button.
Pa
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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
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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
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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
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yp
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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
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yp
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pair&id=AUDI.B5.SU02.01.15

01-294

Output Diagnostic Test Mode (DTM)
-
Operate brake

Indicated on display:
-
Press button.
Output Diagnostic Test Mode (DTM)
-
Ifr: 0V
Ofr: 0V
fr wheel locked

Indicated on display:
-
Press button.
Output Diagnostic Test Mode (DTM)
-
Ifr: B+
Ofr: 0V
fr wheel locked

Indicated on display:
ABS hydraulic pump -V64- must start running.
The brake pedal must not give. -
Press button.
Output Diagnostic Test Mode (DTM)
-
Ifr: B+
Ofr: B+
fr wheel free

Indicated on display:
ABS hydraulic pump -V64- will stop running. -
Press button.
Pa
ge 58 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