Detailed guide for SPN 101 FMI 4
Back to top ↑What SPN 101 FMI 4 means
SPN 101 identifies crankcase pressure. FMI 4 indicates that crankcase pressure sensor voltage is below the calibrated threshold.
Detroit describes SPN 101 FMI 4 as a crankcase pressure sensor circuit failed-low condition.
What to check first
Inspect the crankcase pressure sensor connector and wiring for damaged insulation, corrosion, loose terminals or shorts to ground.
Verify sensor power, ground and signal-circuit continuity using the OEM wiring diagram.
If other FMI 4 sensor faults are active, check shared power or ground circuits before replacing individual sensors.
Diagnostic note
On the documented Detroit application, this is an electrical circuit fault and does not itself command an engine reaction.
A low electrical signal does not automatically prove that actual crankcase pressure is low. Diagnose the circuit before replacing mechanical components.
Mechanic community notes for SPN 101 FMI 4
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