Brake Signal: Testing and Inspection

Special tools, workshop equipment, testers, measuring instruments and auxiliary items required
- VAG1551 scan tool or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
- Test box V.A.G 1598/31
- Hand multi meter V.A.G 1526 or multimeter V.A.G 1715
- Adapter set V.A.G 1594
- Wiring diagram

Test conditions





- Fuse 7 must be OK.

Test sequence
- Connect the VAG1551 scan tool (V.A.G 1552). Then switch ignition on and select engine control unit with the "Address word" 01. (Connecting scan tool and selecting engine control unit.) Testing and Inspection

Indicated on display:

Rapid data transfer HELP
Select function XX

- Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

Indicated on display:

Read measured value block HELP
Input display group number XXX

- Press keys 0, 6 and 6 for "display group 66" and confirm with Q key.

Indicated on display:

Read measured value block 66 ->
1 2 3 4

- Observe display in display zone 2: (3rd and 4th positions from left)
- Specification: x x 0 0
- Depress brake pedal fully and observe display in display zone 2.
- Specification: x x 11
- Press the -> key.
- Press keys 0 and 6 for the "End output" function and confirm input with the Q key.
- Switch off ignition.

If the specification is not obtained:
- Remove the shelf on driver's side.
- Pull the connector off brake light/brake pedal switch.





- Connect multimeter to measure resistance between contacts 1 and 2.
- Specification: Infinity Ohms (no continuity)
- Depress brake pedal.
- Specification: approx. 0 Ohms
- Connect multimeter to measure resistance between contacts 3 and 4
- Specification: approx. 0 Ohms
- Depress the brake pedal.
- Specification: Infinity Ohms (no continuity)

If the specifications are not attained:
- Replace the brake light/brake pedal switch.

If the specifications are obtained:





- Connect multimeter to measure voltage between contact 1 and Ground.
- Specification: at least 11.5 V
- Switch ignition on.
- Connect multimeter to measure voltage between contact 3 and Ground.
- Specification: at least 11.5 V

If the specifications are not obtained:
- Check the wire between 4-pin connector contact 1 and main fuse/contact 2 and central electrics using wiring diagram.
See Electrical Wiring Diagrams, Troubleshooting & Component Locations.

If the specification is obtained:





- Connect test box VAG 1598/31 to control unit wiring harness. The engine control unit remains disconnected.





- Check wiring for open circuit between test box and 4-pin connector using wiring diagram.
- Contact 4 and socket 55
- Contact 2 and socket 56
Wire resistance: Max. 1.5 Ohms
- Additionally check wires for short to one another.
- Additionally check the wiring for short to battery positive or Ground.