SPN 654 FMI 5 — Injector Cylinder 4 Circuit Open
Open circuit on injector 4 requires resistance and continuity proof before replacing the injector.
Fault Overview
SPN 654 is injector cylinder 4. FMI 5 indicates open circuit or current below minimum when the injector is commanded. Detection occurs during actuation when driver current does not rise as expected.
Engine & Platform Coverage
Symptoms
- •Injector cylinder 4 open
- •Cylinder 4 misfire
- •SPN 654 FMI 5
- •No contribution cylinder 4
- •Rough running injector 4
Possible Causes
- 1.Open injector coil
- 2.Broken wire in harness
- 3.Unplugged or high-resistance connector
- 4.Oil-soaked pins
- 5.Failed open driver
Wiring & Circuit Notes
Inspect cylinder 4 injector connector and under-cover harness for oil, pin tension, and chafing. Check pass-through connector integrity. Oil intrusion and under-cover harness damage are the most common open-circuit causes across platforms.
DVOM Specs & Sensor Tests
Coil resistance within platform specification and matched to other cylinders. Continuity from ECM to connector. 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 — Measure Injector 4 Resistance vs Adjacent Cylinders: Measure resistance of injector 4 and compare to adjacent cylinders. Open reads infinite.
- 2Step 2 — Continuity Test ECM to Injector: Continuity test from ECM to injector connector. Identify the open segment.
- 3Step 3 — Inspect Connector for Oil and Pin Fit: Inspect cylinder 4 injector connector and under-cover harness for oil, pin tension, and chafing. Check pass-through connector integrity.
- 4Step 4 — Command and Monitor Current: Command injector and monitor current if scan tool capability is available.
- 5Step 5 — Isolation Swap if Accessible: Isolate by connector swap with an adjacent cylinder if safe and accessible.
- 6Step 6 — Driver Evaluation Last: Evaluate ECM driver only after the external circuit is proven open or good.
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 repair $100–300; connector service $50–150; injector replacement if coil open $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.