Audi Workshop Service and Repair Manuals

The speed signal is required to ensure that the air conditioner compressor is switched off when accelerating. It is also required for the cruise control system and to ensure smoother driving (jolt damping).

Test requirement:

• ● Speedometer OK. Testing:

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

Test sequence

• ‒ Read data block, Display group 006, engine running at idling speed => Page 01-86.
• ‒ Take vehicle for a test drive.

→ Display on VAS 5051:

• ‒ Check display in display zone -1-.
• ‒ Specification: The current road speed should be displayed (compare with speedometer).

• ‒ Press the ◂ button to exit from the function "08 - Read data block".
• ‒ Select diagnosis function "06 - End output".
• ‒ Switch off ignition.

If the specification is not obtained:

• ‒ Connect test box V.A.G 1598/31 to wiring harness for engine control unit.Do notconnect to the engine control unit itself:
• ‒ Connecting test box to engine control unit without protective housing=>Page 23-49.
• ‒ Connecting test box to engine control unit with protective housing=>Page 23-51.
• ‒ Switch on ignition.
• ‒ Raise the vehicle (preferably using a lifting platform) until the front left wheel is clear of the ground.
• ‒ Connect voltage tester V.A.G 1527 B to sockets 4 (earth) and 20 (speed signal) on test box V.A.G 1598/31.
• ‒ Turn the front left wheel.
• ‒ The LED should flash very briefly.

If the LED does not flash:

• ‒ Test for open circuit and short to positive or earth in the following wiring connection:

• ‒ Rectify any open/short circuit as necessary.

If no wiring fault is detected:

• ‒ Establish which systems (e.g. radio, automatic gearbox, air conditioner etc.) are using the speed signal, disconnect them one by one from the dash panel insert, and keep repeating the test until the cause of the problem has been identified.