AUDI A4 2000 B5 / 1.G Brakes Output DTM 03 Workshop Manual

01-149


Output Diagnostic Test Mode
(DTM) (function 03)
Output Diagnostic Test Mode (DTM) is used to
check the function of actuators. Actuators are
also called actors. These are components that
the control module activates when it reacts to the
signals sent by sensors.
"Function of actuators" includes all functions and
properties of an actuator under operating
conditions. This means, for example:

- An electrically operated hydraulic valves that
opens and closes when activated by the control
module.

- The relay of an electrical motor when activated
by the control module. The motor switches on
and carry outs the task.
Before initiating the output Diagnostic Test Mode
(DTM), make sure there are no electrical
malfunctions in the system you wish to test. This
will enable you to recognize any mechanical
problems. Perform a guided troubleshooting
before starting output Diagnostic Test Mode
(DTM) page 01
-19
.
Are you sure there are no electrical malfunctions
in the system? If you have made sure that there
are no electrical malfunctions in the system, you
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gnostic Test Mode
(DTM
) (function 03
)
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will be able to identify any mechanical
malfunctions in the individual actuators if the
results of the output DTM are not as specified
here. Replace the relevant part.
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put Dia
gnostic Test Mode
(DTM
) (function 03
)
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01-150
For Bosch 5.3 ABS/EDL, output Diagnostic Test
Mode (DTM) enables you to check the
electrically actuated hydraulic valves and the
pump motor in the hydraulic module. Also check
whether the brake lines are connected to the
proper brakes.

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. If you wish to perform
output Diagnostic Test Mode (DTM) again after
this, communication must be interrupted via the
"End Output" function page 01
-16
, and then
be re-established.
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put Dia
gnostic Test Mode
(DTM
) (function 03
)
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01-151

Notes:

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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put Dia
gnostic Test Mode
(DTM
) (function 03
)
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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
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put Dia
gnostic Test Mode
(DTM
) (function 03
)
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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.
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put Dia
gnostic Test Mode
(DTM
) (function 03
)
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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.
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gnostic Test Mode
(DTM
) (function 03
)
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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
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put Dia
gnostic Test Mode
(DTM
) (function 03
)
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play?action=Goto&t
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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
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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
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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