SPN 107 FMI 1 — Air Filter Restriction Below Normal
Below-normal restriction readings are housing, hose, and sensor diagnostics. Missed missing-filter or housing seal issues when restriction rationality is ignored is the most documented consequence of skipping this fault class.
Fault Overview
SPN 107 FMI 1 indicates the restriction reading is below the expected minimum — the implausible low class where monitored. Sensor bias low, disconnected sense line, open or short circuit, missing filter element with some strategies, and wiring faults are the primary causes. Physical housing and sense-line integrity must be verified before any sensor replacement.
Engine & Platform Coverage
Symptoms
- •Restriction reading implausibly low on scan tool
- •Restriction sensor stuck at zero or near-zero
- •Restriction code active with filter installed
- •Sense hose disconnected from filter housing
- •Missing filter element with some ECM strategies
Possible Causes
- 1.Sensor bias low producing false low reading
- 2.Disconnected sense line at the filter housing
- 3.Open or short circuit in the restriction sensor wiring
- 4.Missing filter element with some ECM rationality strategies
- 5.Wiring fault at the restriction sensor connector
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
3 steps locked behind Technician Mode- 1Step 1 — Visual Filter and Housing Integrity: Verify the filter element is installed and the housing is properly sealed. A missing filter element or unsealed housing can produce an implausibly low restriction reading with some ECM strategies.
- 2Step 2 — Sense-Line Check: Inspect the sense hose or tube from the filter housing to the restriction sensor. A disconnected or kinked sense line will produce a false low restriction reading.
- 3Step 3 — Sensor Circuit Tests: Perform circuit tests on the restriction sensor — reference voltage, signal voltage, and ground integrity. An open or short circuit will produce an implausible low reading.
- 4Step 4 — Sensor Replacement After Proof: Replace the restriction sensor only after the sense line and circuit are confirmed intact and the sensor itself is proven to be biased low.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
2 steps locked- 1Install missing filter element if absent.
- 2Reconnect disconnected sense hose at the filter housing.
- 3Repair open or short circuit in the restriction sensor wiring.
- 4Replace restriction sensor after circuit proof confirms sensor bias low.
Unlock full diagnostic steps, DVOM tests, and repair procedures.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Start Diagnosing This Fault Now
AI Diesel Tech walks you through every evidence gate in the correct order. Choose the plan that fits your shop.
Related Resources
Related Fault Codes
AI Diesel Tech — The Technician's Diagnostic Engine
AI Diesel Tech diagnostic logic is built by an ASE Certified Diesel Technician and engineered for professional shop use. Trusted by technicians nationwide — used in shops, fleets, and training programs.
Summary
SPN 107 FMI 1 is a housing, sense-line, and sensor diagnosis. Verify filtration integrity and sense-line connection before any sensor replacement.