Brake Light Switch: Testing and Inspection

Brake Light Switch And Brake Pedal Switch, Checking







Special tools and equipment
- VAG1526 A
- VAG1527 B
- VAG1594 A
- VAG1598/31
- VAS5051 with VAS5051/1

NOTE: Command from accelerator pedal sensor (potentiometer) to engine control module for opening throttle valve is suppressed for safety reasons when brake is pressed. For this purpose, the control module requires signals from both the brake light switch and the brake pedal switch.

If the brakes are activated when the accelerator pedal is held at a constant position, the engine speed is immediately reduced to idling speed. Incorrectly adjusted switches may lead to unwanted regulating actions.

Test sequence
- Connect testing and information system VAS5051 and select vehicle system "01 -Engine electronics" in selection. Ignition must be switched on.







Display on VAS5051:
- Under -1- select diagnostic function "08 - Read measured value block".







Display on VAS5051:
1. Enter display group
- Enter "066" for "display group number 066" in zone -2- and confirm entry by pressing -Q- button.







Display on VAS5051:
- Check indication in display field -2-.







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

If the display is not as described:

Check switch
- Remove driver's storage compartment:







- Disconnect connector from brake light/brake pedal switch -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 Ohm

- Press brake pedal.

Specified value: Infinite Ohm (no continuity)

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

If specifications are obtained:

Checking power supply







- Connect voltage tester VAG1527 B as follows:

Connector Measure to
terminal
1 Car body Ground point

- The LED should illuminate.

Connector Measure to
terminal
3 Car body Ground point

- Switch ignition on.
- LED should illuminate.

If the LED does not illuminate:
- Check wiring for open circuit and service if necessary.

If the LED illuminates:

Checking actuation
- Connect test box VAG1598/31 to wiring harness for engine control module; do not connect engine control module. Wiring and Component Check With Test Box VAG 1598/31







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

Connector Test box VAG1598/31
terminal Socket
2 55
4 56

- Repair any open/short circuit as necessary.