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

ARG AVV
Because the injection system operates with an accelerator pedal sender (potentiometer) which may be defective, the engine is throttled back for reasons of safety when the brakes are operated. To do this the control unit 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 by the control unit. Badly adjusted switches can cause the engine to be throttled back when this is not desired.

Connect vehicle diagnostic, testing and information system VAS 5051 (or fault reader V.A.G 1551) and select engine electronics control unit by entering address word "01" ( => Page
01-3
.)
When doing this the ignition must be switched on.

Rapid data transfer
HELP
Select function XX
Indicated on display:

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

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

Press keys 0, 6 and 6 to select Display group 66 and confirm entry with the Q key.

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

Observe display in display zone 2.

Display zones
1 · 2 · 3 · 4
Display group 66: Signals to engine control unit with ignition on
Display · xxx km/h · 0 0 0 0 · xxx km/h · 0 0 0 0
Indicates · Actual speed / · Switch positions · Specified speed · Switch positions for cruise control system
Range · / · off = 0 / on = 1 · / · off = 0 / on = 1
Specification · 0 0 0 0
Note · Relevance of figures => Page 24-175

Depress brake pedal

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

x · x · x · x · Display zone 2
X · Brake light switch / 0 = Brake pedal not depressed / 1 = Brake pedal depressed
X · Brake pedal switch / 0 = Brake pedal not depressed / 1 = Brake pedal depressed
X · Clutch pedal switch / 0 = Clutch pedal not depressed / 1 = Clutch pedal depressed
X · Cruise control system (CCS) / 0 = CCS deactivated / 1 = CCS enabled

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
Indicates · Actual speed / · Switch positions · Specified speed · Switch positions for cruise control system
Range · / · off = 0 / on = 1 · / · off = 0 / on = 1
Specification · 0 0 1 1
Note · Both readouts must change from 0 to 1.

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
=> Page
24-178
.

Testing voltage supply

Remove storage compartment on driver's side.

=> General body repairs, Interior; Repair group 68; Storage compartments, covers and trim parts; Removing and installing driver's storage compartment
General body repairs, Interior
Storage compartments, covers and trim parts
Removing and installing driver's storage compartment

Unplug 4-pin 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 + earth · Battery voltage

Switch ignition on.

4-pin connector on / wiring harness, socket · Specification
3 + earth · Battery voltage

If specifications are met:

Test wiring connections => Page
24-178
.

If specifications are not met:

Test wiring connections from sockets 1 and 3 of connector for open circuit or short to earth.

=> Current flow diagrams, Electrical fault finding and fitting locations binder

Rectify any open/short circuit as necessary.

Checking wiring connections

Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
=> Page
24-10
.

Test the following wiring connections for open circuits and short to positive or earth:

4-pin connector on / wiring harness, socket · Test box V.A.G 1598/31, socket
2 · 56
4 · 55

Resistance in wiring: max. 1.5 ω

=> Current flow diagrams, Electrical fault finding and fitting locations binder

Rectify any open/short circuit as necessary.

If no open circuits are found in wiring:

Renew brake light switch / brake pedal switch.