With Manufacturer's Scan Tool

Brake Light Switch And Brake Pedal Switch, Checking

Special tools and equipment







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

NOTE: 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 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/VAG 1551 Scan Tool (ST)

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, max. entered value =255
- 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 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 4 for resistance measurement.
- Specification: infinite Ohm (no continuity)
- Depress accelerator pedal.
- Specification: approx. 0 Ohm
- Connect multimeter between terminal 2 and 3 for resistance measurement.
- Specification: approx. 0 Ohm
- Depress accelerator pedal.
- Specification: infinite Ohm (no continuity)

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

If specified values are obtained:

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 wire connection from terminal 1 or 2 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
- Connect VAG1598/31 test box at wiring harness to ECM, do not connect ECM. Electrical Testing Using VAG1598/31 Test Box







- Check the following wire 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 or short circuit if necessary.