CAT 3406E (Prefix 1MM or 2WS) Fault Code: 31 PID: SPN: 84 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
![Magic Tuner [paccar, Maxxforce, Detroit, Caterpillar, Delete]](https://www.ecuforcetruck.com/wp-content/uploads/2021/10/1-300x300.png)
