Check brake light switch -F and brake pedal switch -F47 — AUDI

As the injection system operates with an accelerator pedal sender (potentiometer), which could be defective, engine-speed regulation is effected for safety reasons when brake is pressed. The control unit requires the brake-light switch and brake-pedal switch signals for this purpose. In other words, if the brake is actuated with the accelerator pedal constantly pressed, the engine speed is immediately regulated to idling speed. Inaccurate switch settings can lead to unintentional speed regulation.

Connect vehicle diagnostic, testing and information system VAS 5051 or fault reader V.A.G 1551 and select engine electronics control unit with "address word" 01 => Page
01-8
.
Ignition must be on.

Rapid data transfer
HELP
Select function XX
Indicated on display:

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

Read measured value block
Enter display group number XXX
Indicated on display:

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

Read measured value block 66
⇒
1
2
3
4
Indicated on display:

Observe readout in display zone 2.

Display zones
1 · 2 · 3 · 4
Display group 66: Signals to engine control unit
Display · xxx km/h · 0 0 0 0 · xxx km/h · 0 0 0 0
Readout · Vehicle speed / (ACTUAL) · Switch positions · Vehicle speed / (SPECIFIED) · Switch positions for cruise control system
Operating range · / · Off = 0 / On = 1 · / · Off = 0 / On = 1
Specification · 0 0 0 0
Note · Significance of digits / => Page 24-183

Press brake pedal.

Significance of 4-digit display in zone 2:

x · x · x · x · Display zone 2
X · Brake light switch / 0 = Brake pedal not pressed / 1 = Brake pedal pressed
X · Brake pedal switch / 0 = Brake pedal not pressed / 1 = Brake pedal pressed
X · Clutch pedal switch / 0 = Clutch pedal not pressed / 1 = Clutch pedal pressed
X · Cruise control system (CCS) / 0 = CCS disabled / 1 = CCS released

Display zones
1 · 2 · 3 · 4
Display group 66: Signals to engine control unit
Display · xxx km/h · 0 0 1 1 · xxx km/h · 0 0 0 0
Readout · Vehicle speed / (ACTUAL) · Switch positions · Vehicle speed / (SPECIFIED) · Switch positions for cruise control system
Operating range · / · Off = 0 / On = 1 · / · Off = 0 / On = 1
Specification · 0 0 1 1
Note · Both displays must switch from 0 to 1

Allow brake pedal to slowly return to rest position.
Both displays must switch back from 1 to 0.

If one or both of the displays does/do not switch from 0 to 1, check power supply => Page
24-186
.

Checking power supply

Connect portable multimeter for voltage measurement to the following connector sockets:
Switch off ignition.

4-pin connector at wiring harness, socket · Specification
1 + earth · Battery voltage

Switch on ignition.

4-pin connector at wiring harness, socket · Specification
2 + earth · Battery voltage

If readings match specifications:

Check wiring => Page
24-186
.

If readings do not match specifications:

Check for open circuit/short to earth in wiring from sockets 1 and 2 of connector.

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

If necessary, eliminate open circuit in wiring/short circuit.

Checking wiring

Connect test box V.A.G 1598/31 to engine control unit wiring harness. Actual engine control unit is not to be connected=>Page
24-12
.

Check for short to positive/earth and open circuit in the following wiring.

4-pin connector at wiring harness, socket · Test box V.A.G 1598/31, socket
4 · 56
3 · 55

Resistance: max. 1.5 ohms

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

If necessary, eliminate open circuit in wiring/short circuit.

If no open circuit is found in wiring:

Replace brake light switch/brake pedal switch.