Vehicle Speed Signal, Checking

Vehicle speed is required for A/C compressor cut-off during acceleration, for the cruise control system and to improve driving comfort (shift-jerk).

Special Tools, Testers And Auxiliary Items:
- VAG 1551/1552 Scan Tool with VAG 1551/3 adaptor cable
- VAG 1598/22 Test Box
- VW 1594 adaptor kit
- VAG 1527B LED tester
- Wiring diagram

Test Conditions:
- Speedometer Function and Speedometer Display OK

Test Sequence:
- Connect VAG 1551/1552 Scan Tool
- Start engine and let idle
- Press 0 and 1 buttons to select address word 01 "engine electronics"
Display will appear as shown:

Rapid data transfer HELP
Select function XX

- Press 0 and 8 buttons to select Function 08 "Read measuring value block"
- Press Q button to enter input
Display will appear as shown:

Read measuring value block HELP
input display group number XXX

- Press 0, 0 and 6 buttons to select "display group 6"
Press Q button to enter input
Display will appear as shown (1 to 4 = Display zones):

Read measuring value block 6 ->
1 2 3 4

- Perform test drive and observe display during drive

CAUTION: When on the road, measurements are required for diagnosis. For obvious safety reasons always use a second technician to take the instrument readings.

- Observe value shown in display zone 1
Specification: approx. equal to speedometer display.

If no speed indicated:
- Switch OFF ignition





- Connect VAG 1598/18 Test Box to ECM harness connector
- Check wiring for continuity or short circuit between Test Box socket 43 and instrument cluster wiring
- Using Wiring diagram, individually determine all additional speed signal "users" (e.g. radio, automatic transmission, A/C etc.), rule out each one as a source of interference and repeat check each time until cause has been established
- Display the readiness code

If DTC memory was erased:
- Create readiness code again