Brake Light Switch and Brake Pedal Position Switch, Testing

Brake Light Switch And Brake Pedal Position Switch, Testing







Special tools and equipment
- VAG 1526 A
- VAG 1527 B
- VAG 1594 A
- VAG 1598/31
- VAS 5051 with VAS 5051/1

NOTE: For safety reasons, the signal from the accelerator position sensor (potentiometer) instructing the engine control module to open the throttle valve is suppressed whenever the brake is operated. The engine control module therefore needs the brake light signal and also the brake pedal signal.

If the brake is operated while the accelerator is held down at a constant position, the engine is immediately governed down to idling speed. A defective switch can cause the engine to be throttled back when this is not desired.

Test sequence
- Connect the vehicle diagnostic, testing and information system VAS 5051, Vehicle Diagnostic, Testing and Information System VAS 5051, Connecting and Selecting Functions , and select the vehicle system "01 - Engine electronics" from the menu. When doing this the ignition should be switched on.







Display on VAS5051:
- Select the diagnosis function "08 - Read data block" from the menu -1 -.







Display on VAS5051:
1 - Enter display group
(figures up to 255)
- Using the keypad -2-, enter "066" to select Display group 066 and confirm entry with Q button.







Display on VAS5051:
- Check display value for brake light switch / rake pedal position switch (display zone -2-).







- Press the <- button to exit from the function "08 - Read data block".

If the display values do not appear as described:

Testing switches
- Remove storage compartment on driver's side.
- Unplug connector from brake light switch / brake pedal position switch.







- Connect multimeter (resistance measurement range) between contacts 1 and 4.

- Specification: Infinity Ohms (no continuity)

- Depress the brake pedal.

- Specification: approx. 0 Ohm

- Connect multimeter (resistance measurement range) between contacts 2 and 3.

- Specification: approx. 0 Ohm

- Depress the brake pedal.

- Specification: Infinity Ohms (no continuity)

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

If the specifications are obtained:
- Check voltage supply.

Checking voltage supply







- Connect VAG 1527 B voltage tester as follows:

Connector Contact Measure against
1 Body Ground

- The LED should light up.

Connector Contact Measure against
2 Body Ground


- Switch on ignition.
- The LED should light up.

If the LED does not light up:
- Test for open circuit or short to Ground in wiring from contact 1 and/or contact 2 of connector:
- Correct short circuit or open circuit if necessary.

If the LED lights up:
- Test activation.

Checking activation
- Connect test box VAG 1598/31 to wiring harness for engine control module. Do not connect to the engine control module itself.







- Test for open circuit and short to positive or Ground in the following wiring connections:

Connector Contact Test box VAG1598/31 Socket
3 55
4 56

- Correct short circuit or open circuit if necessary.