SPN 654 FMI 6 — Injector Cylinder 4 Circuit Current Above Normal
High current on injector 4 is isolated by resistance measurement and disconnection before parts replacement.
Fault Overview
FMI 6 on SPN 654 indicates current above limit on cylinder 4 injector circuit, consistent with shorted coil or short-to-ground.
Engine & Platform Coverage
Symptoms
- •Injector 4 short
- •Cylinder 4 high current
- •SPN 654 FMI 6
- •Injector short circuit
Possible Causes
- 1.Shorted injector coil
- 2.Harness short to ground
- 3.Incorrect injector resistance
- 4.Oil contamination path
- 5.Damaged insulation
Wiring & Circuit Notes
Inspect under-cover wiring for abrasion and contact with grounded surfaces. Check connector for contamination. Coil shorts and harness abrasion are primary patterns. Always verify correct part number on replacement.
DVOM Specs & Sensor Tests
Resistance near zero indicates short. Disconnect and retest to isolate. Compare to sibling injectors. Peak current will be abnormally high if shorted.
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: Measure resistance of injector 4. Near-zero indicates internal short. Compare to sibling cylinders.
- 2Step 2 — Disconnect and Check Harness for Short to Ground: Disconnect injector 4 and check harness for short to ground. If short clears, the injector is internally shorted.
- 3Step 3 — Inspect for Abrasion: Inspect under-cover wiring for abrasion and contact with grounded surfaces.
- 4Step 4 — Confirm Correct Injector Specification: Confirm correct injector part number and resistance specification. Low-resistance aftermarket units can set overcurrent codes.
- 5Step 5 — Isolate Fault to Single Circuit: Confirm the fault isolates to cylinder 4 and is not a shared circuit issue.
- 6Step 6 — Replace Only the Proven Shorted Component: Replace only the proven shorted component — injector or harness section.
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
Replace shorted injector $300–700; repair harness $100–300. Total $200–800+.
Start Diagnosing This Fault Now
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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.