SPN 662 FMI 6 — Injector Cylinder 12 Circuit Current Above Normal
High-current injector faults are short diagnostics first. Oil intrusion creating intermittent high-current faults and harness damage after in-frame work are the most documented patterns. The FSM protects ECM drivers and prevents replacing good injectors on harness shorts.
Fault Overview
SPN 662 FMI 6 is a cylinder 12 injector circuit current above normal (short class) fault. The ECM driver monitors current during commanded injection and sets FMI 6 when current exceeds the expected range — the driver commanded the injector and saw excessive current. Internal injector shorts, harness shorts, oil-bridged terminals, and pinched looms after service are the primary causes. Oil intrusion creating intermittent high-current faults and harness damage after in-frame work are documented patterns. Protecting ECM drivers from repeated short events is a critical diagnostic priority.
Engine & Platform Coverage
Symptoms
- •Injector 12 shorted
- •Cylinder 12 high current
- •Injector short circuit
- •Misfire from shorted injector
- •ECM driver protection event
Possible Causes
- 1.Internal injector short — internal injector short producing excessive current
- 2.Harness short — harness short to power or ground producing excessive current
- 3.Oil-bridged terminals — oil bridging connector terminals producing short circuit
- 4.Pinched loom after service — loom pinched during in-frame or valve cover service producing short
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 — Disconnect Injector and Isolate: Disconnect the cylinder 12 injector and isolate the harness from the injector. Do not repeatedly actuate a shorted driver. Disconnecting the injector allows the harness to be tested independently from the injector.
- 2Step 2 — Resistance Test at Injector Terminals: Measure resistance at the injector terminals directly. Resistance below OEM minimum supports an internal injector short. Compare to OEM injector specification. An internal short confirmed at the injector terminals justifies injector replacement after circuit proof.
- 3Step 3 — Short-to-Power and Short-to-Ground Check: Check for short-to-power and short-to-ground with the injector disconnected. A short that remains with the injector disconnected confirms a harness fault. A short that clears with the injector disconnected confirms an internal injector fault. Repair the harness before any injector replacement if a harness short is confirmed.
- 4Step 4 — Inspect for Oil Intrusion and Harness Damage: Inspect the connector for oil intrusion and the harness for damage. Oil-bridged terminals produce intermittent high-current faults. Harness damage after in-frame work produces short circuits. Inspect the loom for pinch points near valve cover edges and brackets.
- 5Step 5 — Repair Circuit Before New Injector If Harness Is at Fault: Repair the circuit before any injector replacement if a harness fault is confirmed. A new injector installed into a harness short will fail the new injector and may damage the ECM driver. Confirm circuit integrity before any injector replacement.
- 6Step 6 — Replace Injector with Coding Where Required: Replace the injector with coding or trim where required if an internal short is confirmed. Confirm circuit integrity before the first actuation of the new injector.
- 7Step 7 — Verify After Repair: Verify cylinder 12 operation after repair. Confirm SPN 662 FMI 6 does not return. Monitor for return of high-current events 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 harness short if harness fault is confirmed.
- 2Clean or replace connector if oil intrusion is confirmed.
- 3Replace injector with coding/trim where required if internal short is confirmed.
- 4Inspect and repair loom pinch points after any in-frame service.
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
High-current injector faults are short diagnostics first. The AI Diesel Tech FSM protects ECM drivers and prevents replacing good injectors on harness shorts.