Checking signal from brake light switch and brake pedal switch — AUDI

Special tools, workshop equipment, testers, measuring instruments and auxiliary items required

Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
Test box V.A.G 1598/31
Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
Adapter set V.A.G 1594
Current flow diagram

Test sequence

Connect vehicle diagnostic, testing and information system VAS 5051 and select engine electronics control unit by entering address word "01" (=>Page
01-13
.)
When doing this the ignition must be switched on.
Interrogate fault memory, if necessary, repair fault and then erase fault memory.
=> Page
01-19
, interrogating and erasing fault memory
Then:

Display on VAS 5051:

Select diagnosis function "08 - Read data block" from the menu -1-.

Display on VAS 5051:

1 -
Enter display group
(figures up to 255)

Using the keypad -2-, enter display group number 066 and confirm entry with the Q key (engine must be running at idling speed).

Display on VAS 5051:

Observe display in display zone 2:
(3rd and 4th positions from left)
Specification: x x 0 0
Depress brake pedal fully and observe display in display zone 2.
Specification: x x 1 1
Press←key.
Press the "Go to key" and select the function "End output".
Switch off ignition.

If the specification is not obtained:

Remove the shelf on driver's side:

=> General body repairs, interior; Repair group 68; Dash panel; Removing driver's side shelf
General body repairs, interior
Dash panel
Removing driver's side shelf

Pull the connector off brake light/brake pedal switch.

Connect the multimeter to measure resistance between contacts 1 and 4.
Specification: ∞ ω (no continuity)
Depress brake pedal.
Specification: approx. 0 ω
Connect the multimeter to measure resistance between contacts 2 and 3.
Specification: approx. 0 ω
Depress the brake pedal.
Specification: ∞ ω (no continuity)

If the specifications are not attained:

Replace the brake light/brake pedal switch.

If the specifications are obtained:

Connect multimeter to measure voltage between contact 1 and earth.
Specification: at least 11.5 V
Switch ignition on.
Connect the multimeter to measure voltage between contact 2 and earth.
Specification: at least 11.5 V

If the specifications are not obtained:

Check the wire between 4-pin connector contacts 1 and 2 to central electrics unit using current flow diagram.

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

If the specification is obtained:

Connect test box V.A.G 1598/31 to control unit wiring harness. The engine control unit remains disconnected => Page
24-8
.

Check wiring for open circuit between test box and 4-pin connector for open circuit using current flow diagram.
Contact 3+socket 55
Contact 4+socket 56
Wire resistance: Max. 1.5 ω
Additionally check wires for short to one another.
Additionally check the wiring for short to battery positive or earth.
Rectify short circuit or open circuit if necessary.

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

If no fault is found:

Replace engine control unit
=> Page
24-143
.