Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
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. See DIAGNOSTIC TROUBLE CODE (DTC) MEMORY (SCAN TOOL FUNCTION 02), CHECKING .
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.
- 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 --> 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" See VAG1551 SCAN TOOL (ST), CONNECTING AND ENTERING ADDRESS WORD .
- Check the control module version. See CONTROL MODULE VERSIONS (SCAN TOOL FUNCTION 01), CHECKING and press --> button.
Indicated on display
- Press buttons -0- and -3- to select "Output Diagnostic Test Mode" function 03.
Indicated on display
- Press the -Q- button to confirm input.
Indicated on display
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 --> button.
Indicated on display
- Press --> button.
Indicated on display
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.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.