Brake Light Switch and Brake Pedal Position Switch, Testing

Brake Light Switch And Brake Pedal Switch, Checking







Special tools and equipment
- VAG1526A or Fluke 83 Multimeter
- VAG1527B Voltage tester
- VAG1594A Connector test kit
- VAG1598/31 Test box
- VAS5051 Vehicle diagnosis, testing and information system with VAS5051/1 Adapter

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

Work sequence
- Connect VAS5051 tester, Vehicle Diagnostic, Testing and Information System VAS 5051, Connecting and Selecting Functions and select vehicle system "01 - Engine electronics". Ignition must be switched on.







Display on VAS5051:
- Select diagnostic function "08 - read measured 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.







- Press <- button to end function "08 - Read measuring value block".

If indications do not resemble description:
- Check switch.

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







- Connect multimeter between terminals 1 and 4 for resistance measurement.

- Specified value: Infinity Ohms (no continuity)

- Depress accelerator pedal.

- Specified value: approx. 0 Ohm

- Connect multimeter between terminal 2 and 3 for resistance measurement.

- Specified value: approx. 0 Ohm

- Depress accelerator pedal.

- Specified value: 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:

Harness connector Measure to
Terminal
1 Chassis Ground (GND)

- LED must light up

Harness connector Measure to
Terminal
2 Chassis Ground (GND)

- Switch ignition on.
- LED must light up

If LED does not light up:
- Check wiring connection from terminal 1 or 2 of connector for open circuit and short circuit to Ground (GND)

- Repair open circuit in wiring or short circuit if necessary.

If LED lights up:
- Check activation.

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







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


Harness connector VAG1598/31 test box
Terminal Socket
3 55
4 56

- Repair open circuit in wiring or short circuit if necessary.