Brake Signal: Testing and Inspection

Brake Light Switch And Brake Pedal Switch, Checking


Special Tools and Equipment







- VAG1526A
- VAG1527B
- VAG1594A
- VAG1598/31
- VAS5051 with VAG5051/1


NOTE: For safety reasons, the instruction from the accelerator pedal sensor (potentiometer) to the ECM to open the throttle valve is suppressed when brake is being operated. This requires the brake light switch signal and also the brake pedal switch signal in the control module. If brake pedal is operated with accelerator pedal constantly depressed, engine is immediately regulated down to idle speed. A faulty switch can lead to undesired regulation.


Test sequence
- Connect VAS5051 tester and select vehicle system "01 - Engine electronics". Ignition must remain switched on for this.






Display on VAS5051:
- Select diagnostic function "08 - Read Measuring Value Block" in selection -1-.







Display on VAS5051:
1 - Enter display group Max. input value = 255
- Select function "066" in button field -2- for "Display group number 066" and press Q button to confirm input.







Display on VAS5051:
- Check brake light switch/brake pedal switch in display field -2-.

Display Group 066:

- Press "08 - erase DTC memory" to end function <- button.

If indications do not resemble description:

Check switch
- Remove driver-side storage compartment.
- Disconnect harness connector at brake light switch and brake pedal switch.







- Connect multimeter between terminal 1 and 2 for resistance measurement.
- Specification: Infinity ohms (no continuity)
- Depress accelerator pedal.
- Specification: approx. 0 ohms
- Connect multimeter between terminal 3 and 4 for resistance measurement.
- Specification: approx. 0 ohms
- Depress accelerator pedal.
- Specification: Infinity ohms (no continuity)

If specified values are not obtained:
- Replace brake light switch / brake pedal switch.

If specified values are obtained:
- Check voltage supply

Checking voltage supply






- Connect VAG1527B voltage tester as follows:






- LED must light up.






- Switch ignition on.
- LED must light up.

If LED does not light up:
- Check wire connection from terminal 1 or 3 of connector for open circuit and short circuit to Ground (GND):
- Repair open circuit or short circuit if necessary.

If LED lights up:
- Checking activation.


Checking activation
- Connect VAG1598/31 test box at wiring harness to Engine Control Module (ECM), do not connect ECM.






- Check the following wire connections for open circuit and short circuit to Ground (GND) and B+:






- Repair open circuit or short circuit if necessary.