Testing speed signal — AUDI

AJG ALF
Notes:

The road speed signal is produced by the road speed sender -G68 and processed in the dash panel insert.
The processed signal is sent to the engine control unit and is used for idling speed stabilisation and to damp load change jolts when changing gear.

Connect fault reader V.A.G 1551 (V.A.G 1552) and select engine electronics control unit with the "Address word" 01. When doing this the engine must be running at idling speed.
(Connecting fault reader and selecting engine electronics control unit => Page
01-3
.)

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, 0 and 5 to select Display Group 5 and confirm entry with Q key.

Read measured value block 5
⇒
1
2
3
4
Indicated on display:

Take vehicle for a test drive.

Important:
Secure fault reader to rear seat and operate from this location. When doing this, always observe the relevant safety precautions => Page
24-1
.
Check display value for vehicle speed.

Display zones
1 · 2 · 3 · 4
Display Group 5: Vehicle speed
Display · xxxx rpm · x.xx ms · xxx km/h · Text
Indicates · Actual engine speed / (in steps of 40 rpm) · Engine load · Vehicle speed · Operating status
Range · min.: 600 rpm / max.: 6920 rpm · min.: 0.00 ms / max.: 7.00 ms · min.: 0 km/h / max.: 250 km/h · Idling / part throttle / full throttle / overrun cut-off / acceleration enrichment
Specification · xxxx rpm · 0.00....7.00 ms · current / speed · ---
Note · The display should show the approximate current speed (compare with speedometer / reading). / If readout does not match specification, test wiring / =>Page 24-133

If the vehicle speed is not displayed:

Connect test box V.A.G 1598/22 to wiring harness for engine control unit
=> Page
24-21
.
Test for open circuit and short circuit in wiring between dash panel insert and socket 20 on test box.

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

If no fault in wire is detected:

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