Brake Signal: Testing and Inspection

Signal From Brake Light Switch and Brake Pedal Switch, Checking

Special tools and equipment
- Scan tool VAG 1551 or vehicle system tester VAG 1552 with cable VAG 1551/3
- Test box VAG 1598/31
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram

Test sequence
- Connect the scan tool VAG 1551 (VAG 1552). Then switch ignition on and select engine control module with the "Address word" 01.

(Connecting scan tool and selecting engine control module). Refer to "VAG 1551 Scan Tool" [1][2][3][4][5]Connecting VAG 1551 Scan Tool

Indicated on display:


Rapid data transfer HELP
Select function XX


- Press keys 0 and 8 for 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 1 1
- Press -> key.
- Press keys 0 and 6 for "End output" function and confirm input with Q key.
- Switch off ignition.

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







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

If the specifications are not attained:
- Replace 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 2 and Ground.
Specification: at least 11.5 V

If the specifications are not obtained:
- Check wire between 4-pin connector contact 1 and main fuse/contact 2 and central electrics using wiring diagram.

If the specification is obtained:







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







- Check wiring for open circuit between test box and 4-pin connector for open circuit using wiring diagram.
Contact 3 + socket 55
Contact 4 + socket 56
Wire resistance: Max. 1.5 ohms
- Additionally check wires for short to one another.
- Additionally check wiring for short to battery positive or Ground.