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 throttled back for reasons of safety when the brakes are applied. To do this the control module requires signals from the brake light switch and also 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 un-required regulating process

- Connect vehicle diagnostic, testing and information system VAS5051 or VAG1551 scan tool and select engine electronics control module by entering address word "01". Connecting VAS 5051 Scan Tool
When doing this the ignition must be switched on.

Indicated on display


Rapid data transfer HELP
Select function XX

- Press buttons -0- and -8- to select function "Read Measuring Value Block" and confirm entry with -Q- button.

Indicated on display


Read Measuring Value Block
Input display group number XXX

- Depress brake pedal
- Press buttons -0-, -6- and -6- to select "Display Group 66" and confirm entry with -Q- button.

Display Group 066:

Indicated on display


Read Measuring Value Block 66 ->
1 2 3 4


- Observe display in display field 2.







Relevance of figures in 4-digit readout in display field 2

Display Group 066:

- Allow brake pedal to return slowly to its normal position.
- Both readouts should return from 1 to 0.

If one or both of the displays does not change from 0 to 1:
- Test voltage supply.

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

4-pin connector on wiring harness, socket Specification
1 + Ground (GND) Battery voltage

- Switch ignition on.

4-pin connector on wiring harness, socket Specification
3 + Ground (GND) Battery voltage

If specifications are met:
- Check wiring connections.

If specifications are not met:
- Check wiring connections from sockets 1 and 3 of connector for open circuit or short to Ground (GND).
- Repair any open/short circuit as necessary.

Checking wiring connections
- Connect VAG1598/31 test box to wiring harness for engine control module. Do not connect to the engine control module itself. Connecting VAG 1598/31 Test Box

Test the following wiring connections for open circuits and short to B+ or Ground (GND):

4-pin connector on wiring VAG1598/31 test box,
harness, socket socket
2 56
4 55

Resistance in wiring: max. 1.5 ohm

- Repair any open/short circuit as necessary. If no open circuit is identified in the wiring:
- Replace brake light switch/brake pedal switch.
- Display readiness code. The readiness code must be generated if the DTC memory was erased.
Readiness Code Checking
Readiness Code, Generating