SPN 84 FMI [2,9,10,19] How to Troubleshoot

SPN 84 is a diagnostic trouble code for wheel based vehicle speed data erratic.

FMI 2 – Intermittent Or Incorrect

FMI 9 – Abnormal Update Rate

FMI  10 -Abnormal Rate Of Change

FMI 19 –  Received Network Data In Error

Verify (ECM) electronic control module calibration
Clean (VSS) vehicle speed sensor connections