SPN 660 FMI 6 — Injector Cylinder 10 Circuit Current Above Normal
SPN 660 FMI 6 is a cylinder 10 injector circuit current above normal fault — a short class. High-current injector faults are short diagnostics first. The FSM protects ECM drivers and avoids replacing good injectors on harness shorts.
Fault Overview
FMI 6 on cylinder 10 injector indicates the ECM detected above-normal current on the cylinder 10 injector driver circuit. Internal injector short, harness short to power or ground, oil-bridged terminals, and pinched loom after service are the primary causes. Oil-filled connectors creating intermittent high-current faults and harness damage after in-frame service are documented patterns. Avoid repeated actuation into a shorted circuit — repeated actuation can damage ECM drivers. Disconnect the injector and isolate the harness from the component before any further testing.
Engine & Platform Coverage
Symptoms
- •SPN 660 FMI 6 injector 10 shorted
- •Cylinder 10 high current
- •Injector short to power
- •Misfire from injector short
- •ECM driver protection event cylinder 10
Possible Causes
- 1.Internal injector short — internal injector short circuit producing above-normal current
- 2.Harness short to power or ground — harness insulation damage producing short
- 3.Oil-bridged terminals — oil intrusion bridging terminals in connector
- 4.Pinched loom after service — harness pinched during service producing insulation damage
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 — Inspect for Insulation Rub-Through: Inspect for insulation rub-through on bracket edges and valve-cover corners. A harness that rubs against a sharp bracket edge or valve-cover corner produces insulation damage that creates a short circuit. Inspect the harness routing from the ECM to the cylinder 10 injector for rub-through points.
- 2Binary Decision Gate — Disconnect Injector and Isolate Harness: Disconnect the cylinder 10 injector and isolate the harness from the component. Avoid repeated actuation into a shorted circuit — repeated actuation can damage ECM drivers. Test harness short-to-power and short-to-ground with the injector disconnected to isolate the harness from the component.
- 3Override Manager — Resistance and Short Tests: Perform resistance and short tests on the cylinder 10 injector and harness. A resistance below the OEM minimum specification supports an internal injector short. A short-to-power or short-to-ground confirmed with the injector disconnected confirms a harness fault. A short that clears when the harness is disconnected from the ECM confirms the fault is in the harness, not the ECM.
- 4Safety Interceptor — Repair Circuit Before Installing New Injector: Repair the circuit before installing a new injector if the harness is at fault. Installing a new injector into a shorted harness damages the new injector and the ECM driver. Confirm harness integrity before any injector replacement.
- 5Resume Point — Oil Intrusion Inspection: Inspect for oil intrusion in the cylinder 10 injector connector and harness. Oil-filled connectors creating intermittent high-current faults are a documented pattern. Clean and seal the connector if oil intrusion is found. Identify and correct the oil leak source before returning to service.
- 6Verification Loop — Post-Repair Current Confirmation: After repair, verify cylinder 10 injector circuit current returns to normal. Confirm SPN 660 FMI 6 does not return. Monitor for return of high-current events or driver protection events over extended operation.
- 7Repair Ledger Output — Harness, Connector, or Injector Decision: Repair harness or connector if short circuit is confirmed in the harness path. Replace injector only if internal short is proven after harness integrity is confirmed. Perform injector coding or trim where required by the OEM after replacement. Do not replace the injector for a harness short circuit.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
2 steps locked- 1Repair harness or connector if short circuit is confirmed in the harness path.
- 2Replace injector only if internal short is proven after harness integrity is confirmed.
- 3Perform injector coding or trim where required by the OEM after replacement.
- 4Clean and seal connector if oil intrusion is found.
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.
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Summary
High-current injector faults are short diagnostics first. The AI Diesel Tech FSM protects ECM drivers and avoids replacing good injectors on harness shorts.