SPN 656 FMI 5 — Injector Cylinder 6 Circuit Open
Open on injector 6 requires resistance and continuity proof first.
Fault Overview
SPN 656 FMI 5 indicates open circuit or low current on injector cylinder 6. Detection occurs during actuation when driver current does not rise as expected.
Engine & Platform Coverage
Symptoms
- •Injector cylinder 6 open
- •Cylinder 6 misfire
- •SPN 656 FMI 5
- •No contribution cylinder 6
Possible Causes
- 1.Open coil
- 2.Harness open
- 3.Connector issue
- 4.Oil intrusion
- 5.Open driver
Wiring & Circuit Notes
Cylinder 6 connector, under-cover harness, and pass-through inspection. Oil and chafing remain the leading open-circuit causes across platforms.
DVOM Specs & Sensor Tests
Resistance comparison across all cylinders. Continuity ECM to injector. Current presence during actuation. Open reads infinite resistance.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Step 1 — Resistance vs Siblings: Measure resistance of injector 6 and compare to all other cylinders. Open reads infinite.
- 2Step 2 — Continuity ECM to Injector: Continuity test from ECM driver pins to the injector connector.
- 3Step 3 — Connector Condition: Inspect cylinder 6 connector, under-cover harness, and pass-through for oil, pin tension, and chafing.
- 4Step 4 — Current Check: Command injector and monitor current if scan tool capability is available.
- 5Step 5 — Isolation if Possible: Swap connector with an adjacent cylinder if safe and accessible.
- 6Step 6 — Driver Last: Evaluate ECM driver only after external circuit is proven.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Typical Repair Costs
Harness/connector repair $100–300; injector replacement $300–700. Total $150–700.
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Summary
Use the AI Diesel Tech diagnostic engine to run this code through a structured, evidence-gated sequence and get a confirmed root cause before any parts are replaced.