What does SPN 108 FMI 2 mean on a Freightliner Cascadia?

The barometric-pressure signal is erratic or implausible. The signal helps the engine interpret boost and altitude, so a bad value can affect fueling and performance without proving a mechanical failure.

Can I keep driving with SPN 108 FMI 2?

Treat this as a service-soon condition. Schedule a proper inspection and do not ignore a warning that returns, worsens, or adds a derate.

What should I have ready before checking SPN 108 FMI 2?

Inspect the intake and charge-air path with the engine off and cool. Check the air-filter housing and ducts for loose parts, blockage, or collapse. Use a calibrated pressure reference for any sensor comparison.

SPN 108 FMI 2: The barometric-pressure signal is erratic or implausible