Brake Light Switch -F- and Brake Pedal Switch -F47-, Checking

Brake light switch -F- and Brake pedal switch -F47-, checking

Because the injection system operates with an accelerator pedal sensor (potentiometer) which may be faulty, the engine is regulated for reasons of safety when the brakes are operated. For this purpose, the control module requires signals from both the brake light switch and the brake pedal switch.

This means that if the brakes are operated when the accelerator pedal is held at a constant position, the engine speed is immediately reduced. Incorrectly adjusted switches may lead to undesired control action.

- Connect vehicle diagnostic, testing and information system VAS 5051 or V.A.G 1551 Scan Tool and select engine electronics control module with "Address word" 01. For this purpose, ignition must be switched on.
Connecting VAS 5051 Scan Tool
[1][2]Scan Tool Connecting and Initial Checks

Indicated on display


Rapid data transfer HELP
Select function XX


- Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

Indicated on display


Read measured value block 08
Enter display group number XXX


- Press keys 0, 6 and 6 for "display group number 66" and confirm entry with Q key.

Indicated on display:


Read measured value block 66 ->
1 2 3 4


- Observe readout in display zone 2.

Display Group 66:

- Depress brake pedal.

Meaning of 4 digit readout of display zone 2:

Meaning of 4 digit readout of display zone 2:

Display Group 66:

- Allow brake pedal to return slowly to its normal position.

Both displays should change from 1 back to 0.

If one or both displays do not change:
- Check voltage supply.

Checking power supply

- Remove driver's storage compartment/trim.
- Disconnect 4-pin connector on brake pedal.
- Connect hand-held multimeter (voltage range) between following sockets on the connector:
- Switch ignition off.

4-pin connector on
wiring harness, socket Specified value
1 + Ground Battery voltage

- Switch ignition on.

4-pin connector on
wiring harness, socket Specified value
3 + Ground Battery voltage

If the specified values are attained:
- Check wiring.

If the specified values are not attained:
- Check wiring connections from sockets 1 and 3 of connector for open circuit/short to Ground.
- Correct any open/short circuit as necessary.

Checking wiring
- Connect test box VAG 1598/31 to wiring harness for engine control module; do not connect engine control module. Connecting VAG 1598/31 Test Box
- Check following wiring connections for open circuit and short circuit to positive or Ground.

4-pin connector on
wiring harness, socket Test box VAG 1598/31, socket

2 56
4 55

Wire resistance: max. 1.5 Ohm
- Correct any open/short circuit as necessary.

If no open circuit is detected:
- Replace brake light/brake pedal switch.