FMI 18 — Data valid but below normal operating range — moderately severe level
Real reading, clearly low. The stage before a derate or shutdown.
Common causes
- Leak, restriction on the supply side or worn pump
- Regulator stuck open
- Sensor drift
What to test, in order
- Confirm with a mechanical gauge
- Pressure- or leak-test the supply circuit
- Test the pump and regulator output
- Escalate immediately if the value keeps falling
Codes we document with FMI 18
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