Brake Light and Brake Pedal Switches, Checking

Brake Light and Brake Pedal Switches, Checking

Special tools, testers and auxiliary items required

• Multimeter (V.A.G 1526 A)

• LED voltage tester (VAG1527B)

• Connector test kit (V.A.G 1594 A)

• Test box (VAG1598/31)

• Vehicle diagnostic, testing and information system ( VAS 5051)

• Adapter (VAS 5051/1)

• Command from Sender - 2 - for accelerator pedal position (G185) (potentiometer) to Engine Control Module (ECM) for opening throttle valve is suppressed for safety reasons when brake is pressed. To do so the brake light signal and also the Brake Pedal Switch (F47) signal are required in the ECM. If the brakes are operated when the accelerator pedal is held at a constant position the engine is immediately reduced to idling speed. Incorrectly adjusted switches may lead to unwanted regulating actions.

Work sequence

- Connect scan tool (VAS 5051) and select vehicle system "01 -Engine electronics" in selection. Refer to => [ VAS5051, Connecting and Selecting Functions ] VAS 5051, Connecting and Selecting Functions

When doing this the ignition must be switched on.

Display on (VAS 5051):





- Under - 1 - select diagnostic function "08 - Read measured value block".

Display on (VAS 5051) scan tool:





1. Enter display group

- Enter "066" for "display group number 066" in field - 2 - and confirm entry by pressing Q button.

Display on (VAS 5051) scan tool:





- Check Brake Light Switch (F) / Brake Pedal Switch (F47) in display field - 2 -.





- Exit function "08 - Read measured value block" by pressing arrow button.

If the display is not as described:

Check switch

- Remove driver's storage compartment.

- Disconnect connector from Brake Light Switch ( F) / Brake Pedal Switch (F47) - 2 -.





- Connect multimeter between terminals 1 and 4 to measure resistance.





• Specified value: infinite ohms (no continuity)

- Press brake pedal.

• Specified value: approx. 0 ohms

- Connect multimeter between terminals 2 and 3 to measure resistance.

• Specified value: approx. 0 ohms

- Press brake pedal.

• Specified value: infinite ohms (no continuity)

If the specified values are not obtained:

- Replace Brake Light Switch (F) / Brake Pedal Switch (F47).

If specifications are obtained:

Check power supply

- Connect voltage tester (VAG1527B) as follows:









• LED must light up.





- Switch ignition on.

• LED must light up.

If LED does not light up:

- Check wiring for open circuit and repair if needed.

If LED lights up:

Check activation

- Connect test box (VAG1598/31) to wiring harness for ECM; do not connect ECM. Refer to => [ Electrical Testing, with Test Box VAG 1598/31 ] Electrical Testing, With Test Box VAG 1598/31.

- Check for open circuit and short to positive or Ground (GND) in following wiring connections:









- Repair any open/short circuit as needed.