SPN 677 FMI 6 — Engine Starter Relay Circuit Current Above Normal
SPN 677 FMI 6 means the starter relay control circuit current is above normal — a short class fault. Short isolation is required before installing a new relay — replacing the relay without correcting the short produces repeat failures and risks unintended starter engagement.
Fault Overview
FMI 6 on the starter relay indicates the ECM control circuit is drawing above-normal current. Control wire short to ground or power depending on driver type, failed relay coil short, and water-intruded relay centers are the primary causes. Water entry in relay panels after washes and melted relay bases from chronic overcurrent are documented patterns. Crushed looms near cab mounts and battery boxes are a documented harness short cause. Replacing the relay without isolating the short source produces repeat failures and can create a safety concern if the starter engages unexpectedly.
Engine & Platform Coverage
Symptoms
- •Starter relay circuit short fault active
- •Starter engaged unexpectedly
- •Control circuit high current
- •Relay base heat damage
- •Repeat relay failure
Possible Causes
- 1.Control wire short to ground — insulation damage on control wire
- 2.Control wire short to power — insulation damage creating high-side short
- 3.Failed relay coil short — internal coil short producing low resistance
- 4.Water-intruded relay center — moisture bridging relay terminals
- 5.Crushed loom — loom crushed near cab mount or battery box
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 — Remove Relay and Measure Coil Resistance: Remove the relay and measure coil resistance versus OEM specification. Low coil resistance below the minimum specification confirms an internal coil short. A coil resistance within specification with the relay removed confirms the harness is the short source.
- 2Binary Decision Gate — Control Wire Short Checks: With the relay removed, check the control wire for short-to-ground and short-to-power. Inspect harness near cab mounts and battery boxes for crushed looms. A short on the control wire with the relay removed confirms a harness fault.
- 3Override Manager — Relay Panel and Base Inspection: Inspect the relay panel and base for heat damage from chronic overcurrent. A melted relay base indicates the short has been present for an extended period. Repair the base and panel before installing a new relay.
- 4Safety Interceptor — Water Intrusion Inspection: Inspect the relay center for water intrusion. Water entry in relay panels after washes is a documented cause of high-current relay faults. Inspect relay center seals and address water entry paths before installing a new relay.
- 5Resume Point — Harness Repair Before New Relay: Repair the harness short before installing a new relay. Installing a new relay into a shorted harness produces repeat failure and risks unintended starter engagement.
- 6Verification Loop — Post-Repair Current Confirmation: After repair, verify the relay control circuit current is within normal range. Confirm no unintended starter engagement occurs. Monitor for return of FMI 6 over extended operation.
- 7Repair Ledger Output — Relay, Harness, or Panel Decision: Replace relay if coil short is confirmed. Repair harness short if control wire short is found. Repair relay base and panel if heat damage is found. Address water intrusion source before closing the repair.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
3 steps locked- 1Replace relay if coil short is confirmed.
- 2Repair control wire short-to-ground or short-to-power.
- 3Repair relay base and panel if heat damage is found.
- 4Address water intrusion source in relay center.
- 5Repair crushed loom near cab mount or battery box.
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.
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Summary
High-current starter relay codes require short isolation to prevent repeat failure. The AI Diesel Tech FSM enforces the short-isolation sequence to protect against unintended starter engagement and repeat relay failure.