Brake Light Switch: Testing and Inspection

Signal From Brake Light Switch and Brake Pedal Switch, Checking

Special tools and equipment
- V.A.G 1551 scan tool or 1552 scan tool with cable VAG 1551/3
- Test box VAG 1598/31
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram

Check conditions







- All fuses must be OK.
- The battery voltage must be at least 11.5 V.
- All electrical consumers, e.g. lights and rear window heating must be switched off

Test sequence
- Connect the V.A.G 1551 scan tool ((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 "Scan Tool Connecting Testing/Test Requirements and Work Procedures/VAG 1551 Scan Tool" Testing and Inspection

Indicated on display:


Rapid data transfer HELP
Select function XX


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

Indicated on display:


Read measuring value block
Input display group number XXX


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

Indicated on display:


Read measuring 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 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 the multimeter to measure resistance between contacts 1 and 4.
Specification: Infinity Ohms (no continuity)
- Depress brake pedal.
Specification: approx. 0 Ohms
- Connect the multimeter to measure resistance between contacts 2 and 3.
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.
- Check DTC memory, if necessary, repair any faults and then erase DTC memory, checking and erasing DTC memory. Refer to "Displaying, Reading and Erasing Trouble Codes/With Manufacturers Scan Tool/Clearing Trouble Codes" Testing and Inspection

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 the multimeter to measure voltage between contact 2 and Ground.
Specification: at least 11.5 V

If the specifications are not obtained:
- Check wiring between 4-pin connector contacts I and 2 and multi-function unit using wiring diagram.

If the specification is obtained:
- Remove wiper arms and cowl panel







- 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 using wiring diagram.
Contact 2 and test box socket 55
Contact 4 and test box 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.

If no fault is detected in the pipes:
- Replace engine control module.