SPN 661 FMI 5 — Injector Cylinder 11 Circuit Open
Cylinder 11 injector circuit open is wiring until the injector proves internally open. The ECM driver monitors current during commanded injection and sets FMI 5 when the expected current rise is absent. Service-induced opens after injector R&R and vibration fatigue at flex loops are the most documented patterns.
Fault Overview
SPN 661 FMI 5 is a cylinder 11 injector circuit open/low-current class fault. The ECM driver monitors current during commanded injection and sets FMI 5 when expected current rise is absent — the driver commanded the injector but saw no current response. Unseated connectors, open harness branches, failed injector winding or piezo paths, pass-through pin backouts, and oil or corrosion intrusion are the primary causes. Service-induced opens after injector R&R and vibration fatigue at flex loops are documented patterns. Cylinder-local circuit gates prevent multi-injector shotgun repairs.
Engine & Platform Coverage
Symptoms
- •Injector 11 open circuit
- •Cylinder 11 misfire
- •Injector wiring open
- •No contribution cylinder 11
- •Rough running under load from cylinder 11
Possible Causes
- 1.Unseated connector — cylinder 11 connector not fully seated producing open circuit
- 2.Open harness branch — open in harness branch to cylinder 11 injector
- 3.Failed injector winding or piezo path — internal injector open producing no current response
- 4.Pass-through pin backout — pin backed out at valve cover or ECM pass-through
- 5.Oil or corrosion intrusion — oil or corrosion in connector producing open circuit
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
6 steps locked behind Technician Mode- 1Step 1 — Visual Connector Seat Inspection: Inspect the cylinder 11 injector connector lock and seating. A connector that is not fully seated produces an open circuit that reads identical to a failed injector. Inspect the connector lock, under-cover pass-throughs, and chafe points near brackets and valve-cover edges. Service-induced opens after injector R&R are a documented pattern — always inspect the connector first after any recent injector service.
- 2Step 2 — Resistance Measurement: Measure injector resistance at the connector. Compare to OEM injector specification. An OL or high resistance reading versus OEM spec supports an open circuit. Resistance within spec with a confirmed open circuit at the ECM driver indicates a harness fault between the connector and the ECM.
- 3Step 3 — Continuity to Controller: Verify continuity from the driver connector to the injector connector. A continuity loss confirms an open in the harness path. Inspect the harness for chafe, vibration fatigue at flex loops, and pin backouts at pass-throughs.
- 4Step 4 — Isolate Harness vs Injector: Isolate the fault to the harness or the injector. Disconnect the injector and measure resistance at the injector terminals directly. An OL reading at the injector terminals with a good harness confirms an internal injector open. A good injector resistance with a confirmed harness open confirms a harness fault.
- 5Step 5 — Confirm No Short Before Re-Actuation: Confirm no short-to-power or short-to-ground before re-actuation. Do not repeatedly actuate a circuit with an unresolved fault. Confirm the circuit is clean before any injector actuation test.
- 6Step 6 — Replace Injector Only If Internal Open Proven: Replace the injector only if an internal open is proven at the injector terminals. Injector replacement with coding or trim where required. Do not replace the injector for a harness fault.
- 7Step 7 — Verify After Repair: Verify cylinder 11 contribution after repair. Confirm SPN 661 FMI 5 does not return. Monitor for return of cylinder 11 open circuit faults over extended operation.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
2 steps locked- 1Repair unseated connector or harness open.
- 2Repair pass-through pin backout.
- 3Replace injector with coding/trim where required if internal open is proven.
- 4Clean or replace connector if oil or corrosion intrusion 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
AI Diesel Tech walks you through every evidence gate in the correct order. Choose the plan that fits your shop.
Related Resources
Related Fault Codes
Related Systems
Related Fault Codes
Related Sensor Locations
AI Diesel Tech — The Technician's Diagnostic Engine
AI Diesel Tech diagnostic logic is built by an ASE Certified Diesel Technician and engineered for professional shop use. Trusted by technicians nationwide — used in shops, fleets, and training programs.
Summary
Cylinder 11 open is wiring until the injector proves internally open. The AI Diesel Tech FSM enforces circuit-local gates before injector replacement.