FMI 0 — Data valid but above normal operational range — most severe

The signal is being read correctly and is genuinely too high, at a level the manufacturer classes as most severe. The sensor is fine; the process is not.

Start free J1939 (CAN) → canonical

Diagnosis

When you hit this

Engine coolant temperature above the shutdown threshold, typically reported against SPN 110.
Hydraulic oil temperature exceeding its limit under sustained load.
Overspeed events on SPN 190.

Resolution

How to fix it

Treat it as a real process condition
FMI 0 is not a wiring fault. The measurement is trustworthy and the value is genuinely out of range.
Look up the SPN, not just the FMI
The FMI says how it failed; the SPN says what. SPN 110 with FMI 0 is overheating, and the response is mechanical.
Check for a derate
Most engine controllers derate or shut down on FMI 0, so an unexplained power loss usually has one of these behind it.

Normalization

What Forge does about it

This code is reported by the device itself, so it survives normalization as data. Forge maps the vendor's fault register into the canonical fields alarm_code and alarm_description (and alarm_severity where the vendor supplies one), so an agent reads the same three fields whether the fault came from a Haas, a SINUMERIK, or a Cat engine. Forge does not clear the fault — that is the controller's job.