SPN 651 FMI 5 — Injector Cylinder 1 Circuit Open
SPN 651 FMI 5 means the injector cylinder 1 control circuit is reading open or current is below the normal range. This is a circuit integrity fault — prove the wiring is good before replacing the injector. Oil-intruded connectors under the valve cover are a common cause.
Fault Overview
Electronic injector control circuits are monitored by the ECM for current feedback. FMI 5 (current below normal / open circuit) is set when the ECM cannot drive sufficient current through the injector circuit. This causes a cylinder misfire, rough idle, and power loss. Extended misfire can damage the DPF with unburned fuel. Harness opens and oil-contaminated connectors are more common than injector failure.
Engine & Platform Coverage
Symptoms
- •Cylinder 1 misfire or rough idle
- •Power loss
- •Injector circuit fault active
- •Cylinder contribution imbalance
- •DPF soot loading increase from misfire
Possible Causes
- 1.Open connector — backed-out or corroded pin under valve cover
- 2.Broken injector wire — flex point open at harness loom
- 3.Failed injector coil or piezo circuit — internal open
- 4.Oil intrusion in valve cover connector — corrosion causing open
- 5.ECM driver failure — rare, last resort
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
6 steps locked behind Technician Mode- 1Single Action Gate — Connector Inspection: Remove valve cover and inspect injector connector for oil intrusion, corrosion, or backed-out pins. Oil-soaked connectors are the most common cause of FMI 5 on many platforms.
- 2Binary Decision Gate — Injector Resistance Check: Measure injector coil resistance versus OEM specification. An open reading (infinite resistance) confirms internal injector failure. Within spec means the injector is electrically good.
- 3Override Manager — Harness Continuity Test: With injector disconnected, measure continuity from injector connector to ECM connector. Any open in the harness confirms wiring fault before injector replacement.
- 4Safety Interceptor — Short Checks: Verify no short to ground or power on the injector circuit. Shorts can damage ECM drivers and must be found before reconnecting.
- 5Resume Point — Controlled Swap Test: If OEM procedure allows, swap injector to another cylinder and verify fault follows the injector. Only perform if swap is safe and documented per OEM procedure.
- 6Verification Loop — Post-Repair Circuit Confirmation: After repair, verify injector circuit resistance and continuity are within spec before starting engine.
- 7Repair Ledger Output — Injector Replacement: Replace injector only after circuit is proven good. Note: some platforms require injector coding or trim file programming after replacement.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
3 steps locked- 1Clean and reseat valve cover connector if oil intrusion or corrosion is found.
- 2Repair any harness opens or broken wires found in circuit.
- 3Replace injector if internal coil failure is confirmed.
- 4Program injector trim file or code if required by OEM after replacement.
- 5Seal valve cover connector against future oil intrusion.
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
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Summary
FMI 5 is a circuit open class fault until wiring is proven good. Inspect valve cover connectors, measure injector resistance, and verify harness continuity before replacing the injector. The AI Diesel Tech FSM enforces circuit integrity gates to prevent unnecessary injector replacement.