Brake Signal: Testing and Inspection

Brake Light Switch -F- and Brake Pedal Switch -F47-







Special Tools And Workshop Equipment Required:

- V.A.G 1526 A Multimeter.
- V.A.G 1527 B LED voltage tester.
- V.A.G 1594 A Connector test kit.
- V.A.G 1598/31 Test box.
- VAS 5051.
- VAS 5051/1 Adapter.

NOTE: Command from Throttle Position Sensor 2 -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.

Test sequence

- Connect VAS 5051 scan tool and select vehicle system "01 - Engine electronics" in selection. Connecting VAS 5051 Scan Tool

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-.

Display Group 066:

- Exit function "08 - Read measured value block" by pressing <- 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 Ohm (no continuity).
- Press brake pedal.
- Specified value: approx. 0 Ohm
- Connect multimeter between terminals 2 and 3 to measure resistance.
- Specified value: approx. 0 Ohm
- Press brake pedal.
- Specified value: infinite Ohm(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 V.A.G 1527 B as follows:

Connector Measure to
terminal

1 Car body ground (GND) point.

- LED should light up.

Connector Measure to
terminal

3 Car body ground (GND) point.

- Switch ignition on.
- LED should light up.

If the LED does not light up:
- Check wiring for open circuit and repair if needed.

If the LED lights up:

Check activation

- Connect test box V.A.G 1598/31 to wiring harness for Engine Control Module (ECM); do not connect Engine Control Module (ECM). Wiring and Component Testing Using VAG1598/31 Test Box







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

Connector Test box VAG 1598/31
terminal Socket

2 55
4 56

- Repair any open/short circuit as needed.