Brake Light Switch: Testing and Inspection

Brake Light Switch -F- And Brake Pedal Switch -F47-, Checking

NOTE:
- With the brake pedal pressed, command from the accelerator pedal sender (potentiometer) to the engine control module for opening the throttle valve is suppressed for safety reasons. The control module requires the brake light switch and brake pedal switch signals for this purpose.
- If the brake is actuated with the accelerator pedal constantly pressed, the engine speed is immediately regulated to idling speed. A faulty switch can lead to unintentional speed regulation.

Work sequence

- Connect vehicle diagnostic, testing and information system VAS 5051 and select vehicle system "01 - Engine electronics" from list. Ignition must be on. Connecting VAS 5051 Scan Tool

Indicated on VAS 5051:







- From list -1- select diagnostic function "08 - Reading measured value block".

Indicated on VAS 5051:







1 Enter display group
- Use keypad -2- to enter "066" for "Display group number 066" and confirm by touching Q key.

Indicated on VAS 5051:







- Check display in zone -2-.

Display Group 066:

- Terminate function "08 - Reading measured value block" by touching <- key.

If display is not as described:

Checking switch
- Remove driver's storage compartment.
- Disconnect connector at brake light/brake pedal switch.
- Connect multimeter for resistance measurement between contacts 1 and 4.
- Specification: Infinite Ohm (no continuity)
- Press brake pedal.
- Specification: approx. 0 Ohm
- Connect multimeter for resistance measurement between contacts 2 and 3.
- Specification: approx. 0 Ohm
- Press brake pedal.
- Specification: Infinite Ohm (no continuity)

If readings do not match specifications:
- Replace brake light switch/brake pedal switch.

If readings match specifications:

Checking power supply
- Connect voltage tester V.A.G 1527 B as follows:

Connector Measure to
Contact
1 Body Ground

- LED must light

Connector Measure to
Contact
3 Body Ground

- Switch on ignition.
- LED must light

If LED does not light:
- Check for open circuit in wiring and repair if necessary.

If LED lights:

Checking actuation
- Connect test box V.A.G 1598/31 at wiring harness to engine control module. Actual engine control module is not to be connected. Wiring And Component Check Using Test Box V.A.G 1598/31

- Check for open circuit and short to Ground/positive in following wiring:

Connector Test box V.A.G 1598/31
Contact Socket
2 55
4 56

- Eliminate open circuit in wiring/short circuit if necessary.