With Manufacturer's Scan Tool

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, and select the vehicle system "01 - Engine electronics" from the menu. When doing this the ignition should be switched on. Connecting VAS 5051/VAG1551 Scan Tool






Display on VAS 5051:
- Select the diagnosis function "08 - Read data block" from the menu -1-.






Display on VAS 5051:
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 VAS 5051:
- Check display value for brake light switch / rake pedal position switch (display zone -2-).

Display Group 066:

- 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 ohms

- Connect multimeter (resistance measurement range) between contacts 2 and 3.
- Specification: approx. 0 ohms

- 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 Measure against
Contact
1 Body Ground

- The LED should light up.

Connector Measure against
Contact
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. Wiring and Component Testing Using VAG1598/31 Test Box






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

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

- Correct short circuit or open circuit if necessary.