FMI 21 — Data drifted low
The value crept downward from where it should sit. Slow drift again, most often a tired sensor.
Common causes
- Aging or contaminated sensor
- Slow leak or wear reducing the real value
- Reference voltage low
What to test, in order
- Compare key-off values against ambient reference
- Verify the reference voltage at the sensor
- Trend across trips before condemning the sensor
- Leak- or flow-test the circuit
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