25 March, 2025CAT 3126B Fault Code: 84-01 PID: Flash Code 31 SPN: FMI: Loss of Vehicle Speed Signal A Customer Specified Parameter or a System Configuration Parameter requiring programming has not been programmed. Share on Facebook Opens in a new window. Tweet on Twitter Opens in a new window. Pin on Pinterest Opens in a new window. Back to blog Leave a comment Name * Email * Comment * Please note, comments need to be approved before they are published.