Vehicle Speed Signal (VSS), Checking

NOTE:
- The vehicle speed signal is generated by the Vehicle Speed Sensor (VSS) - G68 - (at transmission) and processed in the instrument cluster
- The processed signal enters at terminal 54 of the ECM and is used for idle stabilization and tip-in shock reduction during shifting.


Test requirement
- Function and display of speedometer OK. Troubleshooting:

Test sequence
- Connect VAS5051 tester or VAG 1551 scan tool and select control module for engine electronics using "address word" 01.
- Engine must run at idle for this.


WARNING!
To reduce the risk of accident during road tests, observe safety precautions. Refer to "Scan Tool (ST) and Test Equipment Safety Precautions - MFI & Ignition System" Technician Safety Information


When indicated on display:


Rapid data transfer HELP
Select function XX


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

When indicated on display:


Read Measuring Value Block Q
Input display group number


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

Indicated on display:


Read Measuring Value Block 5 ->
1 2 3 4


- Determine via road test whether vehicle speed is displayed in display field 3.
- If vehicle speed is not displayed, lift vehicle (if possible using a vehicle lift) until front left wheel is free.
- Connect VAG 1598/31 test box at wiring harness to ECM, do not connect ECM.
- Connect VAG 1527B voltage tester to sockets 3 (B+) and 54 (VSS) of VAG 1598/31 test box.
- Switch ignition on and turn front left wheel by hand.
- LED must blink (very brief blink signal)

If LED does not blink:
- Check the following wire connection for open circuit and short circuit to Ground and B+:

Test box VAG 1598/31 socket Instrument cluster terminal
5

- Repair open circuit or short circuit if necessary.