Brake Light Switch: Testing and Inspection

Signal From Brake Light Switch and Brake Pedal Switch, Checking

Special tools and equipment
- VAG1551 scan tool (or VAG1552 mobile scan tool) with VAG1551/3B cable
- VAG1598/31 test box
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements







- All fuses must be OK.
- Battery voltage must be at least 11.5 volts.

Test sequence
- Connect VAG1551 scan tool (VAG1552). Then switch ignition on and select the Engine Control Module (ECM) using address word 01.

Indicated on display:


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select "Read measuring value block" function 08. Press -Q- button to confirm input.

Indicated on display:


Read measuring value block HELP
Enter display group number XXX


- Press 0, 6 and 6 for the function "display group number 66", and then press Q to exit from input mode.

Indicated on display: (1 to 4 = display fields)


Read measuring value block 66 ->
1 2 3 4


- Observe value indicated in display field 2 (1st and 2nd position from right) Specification: xxxxxx 0 0
- Operate brake pedal and observe value indicated in display field 2. Specification: xxxxxx 1 1
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.

If reading does not change

Test sequence


NOTE: Brake pedal switch -F47- and brake light switch -F- are located together in one housing.


- Disconnect 4-way connector from brake pedal switch and brake light switch.







- Measure resistance between terminals 1 + 4 of switch.
Specified value
Brake not operated: Infinity Ohms
Brake operated: max: 1.5 Ohms

- Measure resistance between terminals 2 + 3 of switch.
Specified value
Brake not operated: max. 1.5 Ohms
Brake operated: Infinity Ohms

If specified values are not obtained:
- Replace brake light switch -F- and brake pedal switch -F47-.

If specified values are obtained:
- Connect multimeter between terminal 1 and Ground (GND) for voltage measurement. Specification: at least 11.5 V







- Connect multimeter between terminal 2 and Ground (GND) for voltage measurement.
- Switch ignition on. Specification: at least 11.5 V

If specified values are not obtained:
- Check wire between 4-pin connector terminals 1 and 2 to central electronics according to wiring diagram:

If specified values are obtained:







- Connect VAG1598/31 test box to control module wiring harness. Engine Control Module (ECM) is not connected.







- Check for open circuits in wire between test box and 4-pin connector according to wiring diagram.
Terminal 3 + socket 55
Terminal 4 + socket 56
Wire resistance: max: 1.5 Ohms
- Check wires for shorts among one another.
- Also check wires for short circuits to B+ or Ground (GND).

After successful repair:
- Read readiness code. If DTC memory was erased or Engine Control Module (ECM) was disconnected from continuous B+ supply, readiness code must be re-generated.