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Output Diagnostic Test Mode (DTM) (Scan Tool Function 03)


The output Diagnostic Test Mode (DTM) can be used to check the function of the components that are actuated by the control module after it processes incoming signal from the sensors.

Notes:Output Diagnostic Test Mode can and must only be selected once after the ignition is switched on.

These check include all functions and properties under operating conditions, for example:
^ Electrically operated hydraulic valves that open and close 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 to be tested. This will enable you to recognize any mechanical problems. Check Diagnostic Trouble Code (DTC) memory before starting the output DTM.

The technician must be sure there are no electrical malfunctions in the system. If the technician has made sure that there are no electrical malfunctions in the system, it will be possible to identify any mechanical malfunctions in the individual actuators if the results of the output DTM are not as specified here. Replace the relevant component.

With the Bosch 5.3 ABS/ESP the output Diagnostic Test Mode (DTM) can be used to check the electrically actuated hydraulic valves and the pump motor in the hydraulic module. It is also possible to check that the brake lines going to the four wheels are connected correctly.

Notes:
^ The vehicle must be raised until all wheels are free to turn. A second technician is required to check whether the wheels are locked or can be turned.
^ 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 output diagnostic test will be terminated if the (arrow) button is not pressed within this period.
^ The ABS warning light and the red brake warning symbol blink during the test.
^ If the brake pedal is pressed repeatedly this will exhaust the vacuum in the brake booster. For this reason, the brake pedal must be pressed harder in order to achieve the same braking effect. It may be advisable to start the engine briefly to build up vacuum in the booster.

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
hyd.pump = Hydraulic pump

- Connect the VAG1551 Scan Tool and select the address word 03 "Brake Electronics".
- Check the control module version and press button.





Indicated on display
- Press buttons -0- and -3- to select "Output Diagnostic Test Mode" function 03.





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- Press the -Q- button to confirm input.





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ABS return flow pump -V39- should start running audibly.





The brake pedal can be felt to vibrate. This is because the hydraulic pump is producing pressure pulses in the brake lines, which induce the vibrations that can be felt at the pedal.
The pressure pulses in the brake lines are not sufficient to lock the wheels





Illustration A01-0015 is a schematic diagram of the hydraulic circuit of an ABS/EDL system. This will give a better understanding of the various test steps in the output Diagnostic Test Mode (DTM).
^ The gray-shaded components are active.
^ 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 (arrow) button.





Indicated on display
- Press (arrow) button.





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When the brake pedal is pressed, brake fluid pressure will be built up in all four calipers. All four wheels will be locked.

This indicates that the mechanical and hydraulic components of the brake system are working properly, which means that the master cylinder is able to build up pressure in all four calipers and there are no leaks in the hydraulic lines, hoses, and connections.





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 (arrow) button.





Indicated on display
Keep pressing brake pedal.





The inlet valve is activated, which interrupts the brake line. However, the fluid pressure is still maintained in the caliper. 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 (arrow) button.





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 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 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 (arrow) button.





Indicated on display
ABS return flow pump -V39- 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, it should be possible 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 (arrow) button.





Indicated on display





Keep pressing brake pedal. The inlet valve is no longer activated and does not interrupt the brake line. The brake pedal will give perceptibly under foot. Fluid pressure is built again in the left front caliper. The wheel will be locked.
- Press (arrow) button.





Indicated on display
- Press (arrow) button.
Continue the output diagnostic test mode in order to check the right-front, left-rear, and right-rear wheels in turn. The test steps are the same as for the left-front wheel, so they are not described in detail.





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- Press (arrow) button.





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- Press (arrow) button.





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- Press (arrow) button.
ABS return flow pump -V39- should start running.
The brake pedal must not give.





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- Press (arrow) button.
ABS return flow pump -V39- will stop running.





Indicated on display
- Press (arrow) button.
The brake pedal will give perceptibly under foot.





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- Press (arrow) button.





Indicated on display
- Press (arrow) button.





Indicated on display
- Press (arrow) button.





Indicated on display
- Press (arrow) button.





Indicated on display
- Press (arrow) button.
ABS return flow pump -V39- should start running.
The brake pedal must not give.





Indicated on display
- Press (arrow) button.
ABS return flow pump -V39- will stop running.





Indicated on display
- Press (arrow) button.
The brake pedal will give perceptibly under foot.





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- Press (arrow) button.





Indicated on display
- Press (arrow) button.





Indicated on display
- Press (arrow) button.





Indicated on display
- Press (arrow) button.





Indicated on display
- Press (arrow) button.
ABS return flow pump -V39- should start running.
The brake pedal must not give.





Indicated on display
- Press (arrow) button.
ABS return flow pump -V39- will stop running.





Indicated on display
- Press (arrow) button.
The brake pedal will give perceptibly under foot.





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- Press (arrow) button.





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- Press (arrow) button.





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The EDL change-over valve (left) and the EDL inlet valve are activated. ABS return flow pump -V39- runs for one second. The pump draws brake fluid out of the fluid reservoir via the EDL inlet valve and builds up pressure in the EDL controlled calipers. These wheels will then be locked.
If not, this indicates a mechanical malfunction in one of the valves, providing there is no electrical malfunction in the system. Replace hydraulic control unit.
- Press (arrow) button.





Indicated on display:

Note: The output diagnostic test mode is completed. The ABS warning light and the red warning symbol for brake system go out.

- Press (arrow) button.





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Note: If the ABS warning light does not go out, this indicates a malfunction in the system. Follow the procedure exactly.

- Press buttons -0- and -6- to select "End Output" function 06. Press -Q-button to confirm input.
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