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