Brake Light Switch and Brake Pedal Switch, Checking

NOTE: The Diesel injection system operates using a Throttle Position sensor For safety reasons, engine speed is limited when the brakes are operated. The ECM accomplishes this by using the signals from the brake light and brake pedal switches. This means that if the brakes are operated while the accelerator pedal is held at a constant position the engine is immediately reduced to idle speed. Incorrectly adjusted switches could lead to unwanted regulating action


Special tools, workshop equipment, testers, measuring instruments and auxiliary items required
- VAG 1551/1552 Scan Tool using VAG 1551/3 adaptor cable
- VAG 1598/22 Test Box
- Fluke 83 multimeter
- VW 1594 Adaptor kit
- Wiring diagram

Test sequence

- Connect VAG 1551/1552 Scan Tool. Testing and Inspection
- Ensure that ignition is switched ON

- Press 0 and 1 buttons to select Address word 01: "Engine electronics"

Display will appear as shown


Rapid data transfer HELP
Select function XX

- Press 0 and 8 buttons to select Function 08: "Read measuring value block"
- Press Q button to enter input

Display will appear as shown


Read measuring value block HELP
Input display group number block


- Press 0, 0 and 6 buttons to select "Display group 6"
- Press Q button to enter input
- Observe value in display zone 2.

Specification: 0 0 0


Read measuring value block 6 ->
0 km/h 000 000000 255


- Operate brake pedal slowly.


Specification: 0 1 1

- Both displays must change from 0 to 1 at same time.
- Center display Brake pedal switch
- Right-hand display = Brake light switch


Read measuring value block 6 ->
0 km/h 011 000000


- Slowly release brake pedal to rest position again.

- Both displays must change from 1 to 0 again.


Read measuring value block 6 ->
0 km/h 000 000000 255


If one or both displays do not change:
- Check switches and switch wiring.
See Wiring diagrams, Electrical Troubleshooting and Component Locations.