display AUDI A4 1995 B5 / 1.G Brakes Output DTM 03 Workshop Manual

01-152

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 5 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
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play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13

01-153

- Connect the VAG1551 Scan Tool (ST) and
select address word 03 "Brake Electronics".

- Check the control module version page 01
-
128
and press the button.
Rapid data transfer
HELP
Select function XX

Indicated on display:
- Press buttons -0- and -3- to select "Output Diagnostic Test Mode
(DTM)" function 03.
Rapid data transfer
Q
03 - Output Dia
gnostic Test Mode
(DTM
)

Indicated on display:
- Press -Q- button to confirm input.
Pa
ge 6 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13

01-154

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

Indicated on display:
ABS/EDL 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.
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
ge 7 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
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p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13

01-155

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. 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.
Pa
ge 8 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13

01-156

-
Press button.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 9 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13

01-157

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.
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 control 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 10 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13

01-158

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

Indicated on display:
ABS/EDL 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 11 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13

01-159

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

Indicated on display:

Keep pressing brake pedal. Inlet valve is no longer being activated. It is
no longer interrupting the brake line. The brake pedal will give perceptibly
under your foot. Fluid pressure is built again in the left-front caliper. The
wheel will be locked.
-
Press button.
Output Diagnostic Test Mode (DTM)
-
Release brake

Indicated on display:
-
Press button.
Pa
ge 12 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13

01-160

Continue output Diagnostic Test Mode (DTM)
in order to check the front right, rear left, and
rear right wheels in sequence. The test steps
indicate the procedure for the front left wheel.
They will therefore not be repeated in detail. 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/EDL 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/EDL hydraulic pump -V64- will stop running. -
Press button.
Pa
ge 13 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13

01-161

Output Diagnostic Test Mode (DTM)
-
Ifr: B+
Ofr: 0V
fr wheel free

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

Indicated on display:
-
Press button.
Output Diagnostic Test Mode (DTM)
-
Release brake

Indicated on display:
-
Press button.
Output Diagnostic Test Mode (DTM)
-
Operate brake

Indicated on display:
-
Press button.
Output Diagnostic Test Mode (DTM)
-
Irl 0V
Orl: 0V
rl wheel locked

Indicated on display:
-
Press button.
Output Diagnostic Test Mode (DTM)
-
Irl B+
Orl: 0V
rl wheel locked

Indicated on display:
ABS/EDL hydraulic pump -V64- must start running.
The brake pedal must not give. -
Press button.
Pa
ge 14 of 66 Out
put Dia
gnostic Test Mode
(DTM
) (function 03
)
11/20/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.SU02.01.13