FMI 2 — Data erratic, intermittent or incorrect
The ECM is getting a signal but it jumps around or does not make sense. Nine times out of ten this is a connection, not a part.
Common causes
- Chafed or loose wiring, spread or corroded pins
- Failing sensor element
- Loose ground or shared ground with a high-draw device
- Interference from a poorly routed harness
What to test, in order
- Wiggle-test the harness and connector while watching live data
- Pull the connector and inspect for green pins, backed-out terminals and pushed seals
- Check the ground path resistance to battery negative
- Data-log the parameter over a road test to catch the dropout
Codes we document with FMI 2
SPN 84 FMI 2Vehicle speed sensor erratic · VolvoSPN 108 FMI 2Barometric pressure sensor erratic · MackSPN 191 FMI 2Transmission output speed erratic · All makesSPN 597 FMI 2Brake switch circuit fault · PACCARSPN 639 FMI 2J1939 data link error · All makesSPN 3251 FMI 2DPF pressure data erratic with high restriction · MackSPN 3364 FMI 2DEF quality poor · PACCARSPN 3364 FMI 2DEF quality below threshold · Volvo
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