SPN 1675 FMI 5 — Engine Starter Mode / Relay Enable Circuit Open
Starter enable open codes are interlock and control-path diagnostics. No-crank caused by a range sensor or clutch switch rather than starter motor failure is the most documented pattern. The FSM enforces interlock-first no-crank diagnosis.
Fault Overview
SPN 1675 FMI 5 indicates a starter enable or mode circuit open class depending on OEM mapping of starter control logic. Open enable wire, failed interlock switch, neutral safety open, clutch switch open, and poor ignition feed are the primary causes. No-crank caused by a range sensor or clutch switch rather than starter motor failure is a documented pattern. Replacing the starter motor before proving the enable and interlock path is the most documented misdiagnosis pattern.
Engine & Platform Coverage
Symptoms
- •Starter enable open
- •Starter mode circuit fault
- •No crank enable signal
- •Interlock open circuit
- •No-crank from range sensor or clutch switch
Possible Causes
- 1.Open enable wire — open enable wire producing open circuit on starter enable path
- 2.Failed interlock switch — failed interlock switch producing open enable circuit
- 3.Neutral safety open — neutral safety switch open producing no enable signal
- 4.Clutch switch open — clutch switch open producing no enable signal
- 5.Poor ignition feed — poor ignition feed producing open enable circuit
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
3 steps locked behind Technician Mode- 1Step 1 — Verify Range/Clutch Status: Verify range and clutch status. Confirm enable status PIDs match actual range and clutch state. No-crank caused by a range sensor or clutch switch rather than starter motor failure is a documented pattern. Confirm the transmission range sensor and clutch switch are reporting correctly.
- 2Step 2 — Check Enable Voltage Path: Check the enable voltage path. Measure enable voltage during a start request. A poor ignition feed producing an open enable circuit requires ignition feed diagnosis. Verify enable voltage is present at the enable relay or ECM enable input during a start request.
- 3Step 3 — Switch Continuity: Check switch continuity. Verify continuity through the interlock switches — neutral safety, clutch switch, and any other enable switches in the circuit. A failed interlock switch producing an open enable circuit confirms a switch fault.
- 4Step 4 — Relay/Starter Power Tests Only After Interlock Proof: Perform relay and starter power tests only after interlock proof. Confirm range/clutch status, enable voltage path, and switch continuity before any relay or starter power-side assessment. A starter replaced before proving the enable and interlock path will not resolve an enable circuit fault.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
3 steps locked- 1Replace failed interlock switch if confirmed.
- 2Replace range sensor if failure is confirmed.
- 3Repair open enable wire if confirmed.
- 4Repair ignition feed if poor feed is confirmed.
- 5Service relay as needed after enable path is proven.
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
Starter enable open codes are interlock and control-path diagnostics. The AI Diesel Tech FSM enforces interlock-first no-crank diagnosis.