Vehicle Speed Signal, Checking

Vehicle speed signal, checking

Required special tools and test equipment
- VAG 1551 or VAG 1552 Scan Tool (ST) with VAG 1551/3 adapter cable
- Multimeter US 1119 (Fluke 83 or equivalent)
- VW 1594 connector test kit
- Wiring diagrams

Test conditions
- Vehicle Speed Sensor (VSS) OK; checking:

NOTE:
- To check Vehicle Speed Sensor (VSS) -G68- the vehicle must be driven. A second technician is required to operate the scan tool during the road test.
- Read safety precautions for test driving vehicles while using test equipment.
- The speed signal is generated by the vehicle speed sensor (at the transmission), and processed at the speedometer/odometer in the instrument cluster.

Test procedure
- Connect VAG 1551 or VAG 1552 scan tool and press buttons -0- and -1- to insert "Engine Electronics" address word 01 (with engine running at idle).Refer to "Scan tool Testing/Scan Tool Connecting and Initial Checks/Connecting VAG 1551/VAG 1552 Scan Tool" Testing and Inspection


Indicated on display


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select "Read Measuring Value Block" function 08, and press -Q- button to confirm input.

Indicated on display


Read Measuring Value Block HELP
Input display group number XXX


- Press buttons -0-, -0- and -5- to input display group number 5 (005), and press -Q- button to confirm input.

Indicated on display (1-4 = display fields)


Read Measuring Value Block 5 ->
1 2 3 4


- Road test and compare indicated vehicle speed with value in display field 3 (2nd technician required, See Safety precautions).

Display Group 5:

If displayed value is OK:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06, and press -Q- button to confirm input.
- Switch ignition off.

Continuation
If no speed was indicated:







- Connect VAG 1598/22 test box to ECM harness connector. Connecting VAG 1598/22 Test Box
- Connect VAG 1527B LED voltage tester between ECM/test box sockets 3 (B+) and 20 (signal).
- Lift vehicle at left-front until wheel is free.
- Switch ignition on and rotate left-front wheel by hand.
LED must blink (very brief blink)


NOTE:
- The right-front wheel must not rotate; block it if necessary.
- For LEDs with little voltage consumption, the LED lights up at half strength when the ignition is switched on.


If the LED does not blink:
- Check wiring from ECM connector, terminal 20 to instrument cluster for open circuit or short circuit:

If the wiring is OK and the LED does not blink:
- Check readiness code. If Diagnostic Trouble Code (DTC) memory has been erased, or ECM was disconnected, generate new readiness code. Audi Drive Cycle/Readiness Code