SPN 666 FMI 5 — Injector Cylinder 16 Circuit Open
Cylinder 16 open is a localized electrical diagnosis. The FSM prevents 'replace all injectors' behavior on one-circuit faults. Overlooked connector not fully locked after major service is the most documented pattern.
Fault Overview
SPN 666 FMI 5 is a cylinder 16 injector circuit open class fault. Connector open, harness open, injector internal open, and pass-through terminal exit failure are the primary causes. Overlooked connector not fully locked after major service is a documented pattern — harder-access connectors are often disturbed during major engine dress service. Broad injector service for a single-circuit fault is the most documented misdiagnosis pattern.
Engine & Platform Coverage
Symptoms
- •Injector 16 open circuit
- •Cylinder 16 dead miss
- •No contribution cylinder 16
- •Smoke or roughness under load
- •Contribution imbalance
Possible Causes
- 1.Connector open — connector open at cylinder 16 producing open circuit
- 2.Harness open — harness open in cylinder 16 branch
- 3.Injector internal open — injector internal open producing open circuit
- 4.Pass-through terminal exit failure — pass-through terminal exit failure producing open circuit
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 — Access and Inspect Connector: Access and inspect the cylinder 16 connector. Harder-access connectors are often disturbed during major engine dress service. Overlooked connector not fully locked after major service is a documented pattern. Confirm the connector is fully seated and locked.
- 2Step 2 — Electrical Measurements: Perform electrical measurements. Measure injector resistance against OEM specification. Check continuity from the driver to the injector. The resistance and continuity process is identical to other cylinder open faults — use OEM specifications as the standard.
- 3Step 3 — Safe Comparison to Adjacent Cylinders: Compare to adjacent cylinders as a reference only. Use OEM specifications as the standard. A resistance or continuity fault on cylinder 16 that is not present on adjacent cylinders confirms a cylinder 16 specific fault.
- 4Step 4 — Single-Circuit Isolation Before Broad Service: Isolate the single circuit before any broad injector service. A single-circuit fault does not require broad injector service. Repair the harness or connector if a harness fault is confirmed. Replace the injector only if an internal open is confirmed after circuit proof.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
1 steps locked- 1Repair harness or connector if open circuit is confirmed in the harness.
- 2Replace injector if internal open is confirmed after circuit proof.
- 3Repair pass-through terminal if exit failure is confirmed.
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
Cylinder 16 open is a localized electrical diagnosis. The AI Diesel Tech FSM prevents 'replace all injectors' behavior on one-circuit faults.