The ECM detects the following conditions:

•The vehicle speed signal indicates a constant MPH.
•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