CAT 3406E (Prefix 5DS or 1LW) Fault Code: 31 PID: 84 SPN: FMI: 1 Vehicle Speed loss of signal

The ECM detects the following conditions:

•The vehicle speed signal indicates that the vehicle speed is 0 MPH.
•Desired engine speed is greater than the programmed “VSL Protection”.
•The “VSL Protection” parameter is programmed to a value that is less than 2120 rpm.

Probable Causes:

1) Fuel system restriction (Uncommon, but possible)
2) If speedometer is not accurate, then ECM is not programmed correctly
3) Vehicle speed sensor
4) Vehicle speed sensor wiring
5) ECM Connection/Harness
6) Speedometer failure
7) ECM Failure