SPN 653 FMI 6 — Injector Cylinder 3 Circuit Current Above Normal
High current on injector cylinder 3 is a shorted coil or harness short. Isolate by resistance and disconnection before replacement.
Fault Overview
FMI 6 indicates current above the calibrated high limit on the cylinder 3 injector circuit. The ECM detects a shorted coil or short-to-ground on the driver side when the injector is actuated or during circuit checks.
Engine & Platform Coverage
Symptoms
- •Injector 3 short
- •Cylinder 3 high current
- •SPN 653 FMI 6
- •Injector circuit overload
- •Misfire with short code
Possible Causes
- 1.Shorted injector coil
- 2.Control wire shorted to ground
- 3.Damaged insulation under the valve cover
- 4.Incorrect injector installed with wrong resistance
- 5.ECM driver short (rare)
- 6.Oil contamination creating low-resistance path
Wiring & Circuit Notes
Inspect for pinched or chafed wires under the valve cover and at the pass-through. Check for insulation damage that allows contact with grounded metal. Internal coil shorts after thermal cycling or manufacturing defects are common. Harness abrasion under the cover is a frequent external short source.
DVOM Specs & Sensor Tests
Injector resistance near 0 Ω indicates internal short. Measure resistance at the connector and compare to other cylinders. Disconnect injector and recheck circuit current or resistance to isolate injector vs wiring. 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 3 Resistance: Measure resistance of injector 3 and compare to sibling cylinders. Near-zero resistance indicates an internal short.
- 2Step 2 — Disconnect Injector 3 and Recheck: Disconnect injector 3 and recheck for short to ground on the harness side. If the short clears, the injector coil is shorted internally.
- 3Step 3 — Inspect Under-Cover Harness for Abrasion: Inspect under-valve-cover harness for pinched or chafed wires and insulation damage that allows contact with grounded metal.
- 4Step 4 — Verify Correct Injector Part Number: Verify correct injector part number and resistance specification. Low-resistance aftermarket units can set overcurrent codes.
- 5Step 5 — Confirm Fault Isolates to Cylinder 3: Command remaining injectors to confirm the fault isolates to cylinder 3 and is not a shared circuit issue.
- 6Step 6 — Replace Only the Proven Shorted Component: Only after isolation, replace the shorted component — injector or harness section as proven.
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 with correct OEM-spec unit $300–700; repair shorted harness section $100–300; replace damaged connector $50–150. Total $200–800+ depending on injector price and labor access.
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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.