SPN 651 FMI 6 — Injector Cylinder 1 Circuit Current Above Normal
SPN 651 FMI 6 is a high-current class fault on the cylinder 1 injector driver circuit, indicating a short-to-power or low-resistance short condition. Isolate the short before any injector replacement — and never repeatedly command a shorted driver, as this risks ECM driver damage.
Fault Overview
FMI 6 on the injector circuit indicates the ECM driver is seeing above-normal current, which is the short or low-resistance class. A shorted injector coil or piezo path, harness short to power, oil-intruded connector bridging pins, and damaged pass-through connectors are the primary causes. Valve-cover connector oil migration causing intermittent shorts is a documented pattern on multiple platforms. Replacing the injector without isolating the short first risks damaging the ECM driver if the short is in the harness rather than the injector. Do not repeatedly command a shorted driver.
Engine & Platform Coverage
Symptoms
- •Injector cylinder 1 circuit high current fault active
- •Cylinder 1 misfire
- •Rough idle from cylinder 1 contribution loss
- •Rail pressure instability from injector fault
- •Possible ECM driver damage if short is not isolated
Possible Causes
- 1.Shorted injector coil or piezo path — internal injector failure
- 2.Harness short to power — insulation damage or chafe
- 3.Oil-intruded connector bridging pins — valve-cover connector oil migration
- 4.Damaged pass-through connector — pin-to-pin short
- 5.Pinched loom at bracket — insulation damage from installation
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 — Disconnect Injector and Remeasure Circuit: Disconnect the cylinder 1 injector and remeasure the circuit. If the high-current condition clears with the injector disconnected, the fault is in the injector. If the high-current condition persists with the injector disconnected, the fault is in the harness. This is the mandatory first isolation step — do not repeatedly command a shorted driver.
- 2Binary Decision Gate — Resistance Check: Measure resistance across the injector terminals. Resistance below OEM minimum specification supports an internal short. Compare to OEM injector resistance specification for the specific injector type (solenoid vs piezo values differ significantly).
- 3Override Manager — Short-to-Power and Short-to-Ground Tests: Test for short to battery voltage and short to ground on the injector circuit harness. Inspect under-cover injector connectors for oil contamination, pinched looms, and rubbed insulation at brackets.
- 4Safety Interceptor — Harness Isolation: Inspect valve-cover connector for oil migration. Oil migrating through the valve-cover connector can bridge pins and create intermittent shorts that appear to be injector failures. Inspect the full harness run from pass-through to injector connector.
- 5Resume Point — Pass-Through Connector Inspection: Inspect the injector harness pass-through connector for pin-to-pin shorts. Damaged pass-through connectors are a documented cause of injector circuit shorts that affect multiple cylinders.
- 6Verification Loop — Post-Repair Circuit Confirmation: After repair, verify circuit resistance is within OEM specification. Confirm no short-to-power or short-to-ground conditions remain. Verify cylinder 1 contribution returns to normal after repair.
- 7Repair Ledger Output — Injector or Harness Decision: Replace injector after circuit isolation confirms internal short. Repair harness if short is in the wiring. Replace injector with coding or trim where required by OEM procedure.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
3 steps locked- 1Repair harness short if found in wiring.
- 2Clean or replace valve-cover connector if oil migration is found.
- 3Repair pass-through connector if pin-to-pin short is found.
- 4Replace injector after circuit isolation confirms internal short.
- 5Code or trim replacement injector per OEM procedure where required.
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
SPN 651 FMI 6 is a short-circuit diagnosis before injector replacement. The AI Diesel Tech FSM protects ECM drivers by stopping repeated actuation into a shorted circuit and enforcing harness isolation before any injector decision.