SPN 1081 FMI 5 — Wait-to-Start Lamp Circuit Open
Open wait-to-start lamp circuit is usually the bulb or a simple wiring open. Prove continuity before any module work.
Fault Overview
FMI 5 indicates an open circuit in the wait-to-start lamp control path. The ECM detects that the circuit does not respond as expected when the lamp is commanded.
Engine & Platform Coverage
Symptoms
- •Wait-to-start lamp open circuit fault active
- •Glow plug light inoperative
- •Lamp circuit open condition
Possible Causes
- 1.Open control wire
- 2.Failed open bulb or LED
- 3.Unplugged connector
- 4.Open driver
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
4 steps locked behind Technician Mode- 1Step 1 — Check Bulb/LED Continuity: Measure bulb resistance or LED continuity. An open bulb reads infinite resistance and is the most common cause of an open lamp circuit.
- 2Step 2 — Continuity Test Control Wire End to End: Perform end-to-end continuity test on the control wire from ECM to lamp socket. An open wire reads infinite resistance.
- 3Step 3 — Verify Connector Pin Tension: Inspect connectors at the cluster and ECM for backed-out pins. A backed-out pin creates an open circuit that reads as a wiring fault.
- 4Step 4 — Measure Voltage at ECM Output and Lamp Side: Measure voltage at the ECM output terminal and at the lamp socket. Voltage present at ECM but absent at lamp confirms an open in the wiring between them.
- 5Step 5 — Confirm Driver Operation: If the circuit is intact but the lamp does not illuminate, confirm ECM driver operation. A failed open driver will not produce voltage or pull-down regardless of command.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
2 steps locked- 1Replace failed open bulb.
- 2Repair open control wire.
- 3Restore connector with backed-out or corroded pins.
- 4Repair ECM driver circuit only after external circuit is proven good.
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
Open wait-to-start lamp circuit is usually the bulb or a simple wiring open. Prove continuity before any module work.