SPN 723 FMI 4 — Camshaft Speed / Position Circuit Voltage Below Normal
CMP low-voltage codes need short isolation before gear-train conclusions. Intermittent sync loss from shorted CMP circuits after service is the most documented consequence.
Fault Overview
SPN 723 FMI 4 indicates the camshaft speed or position sensor circuit voltage is below the valid minimum — a short circuit or low-signal class fault. Signal short to ground, failed sensor with internal short, crushed harness near front cover or gear housing, and oil or moisture bridging are the primary causes.
Engine & Platform Coverage
Possible Causes
- 1.Signal wire short to ground at cover-edge pinch points
- 2.Failed CMP sensor with internal short to ground
- 3.Crushed harness near front cover or gear housing
- 4.Oil-soaked connector bridging signal to ground
- 5.Moisture bridging at CMP sensor connector
Wiring & Circuit Notes
Inspect cover-edge pinch points and oil-soaked connectors — these are the highest-probability short locations for the CMP circuit. Disconnect isolation identifies whether the short is in the sensor or the harness.
DVOM Specs & Sensor Tests
Disconnect the CMP sensor and check the signal wire for short to ground. If the short clears with the sensor disconnected, the sensor is internally shorted. If the short persists, inspect the harness at cover-edge and bracket chafe points. After repair, confirm CMP signal activity while cranking before returning to service. Evaluate tone wheel and mechanical issues only after clean signals are confirmed.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
6 steps locked behind Technician Mode- 1Disconnect CMP sensor connector
- 2Check signal wire for short to ground with sensor disconnected
- 3If short clears with sensor disconnected — replace CMP sensor
- 4If short persists — inspect harness at cover-edge and bracket chafe points
- 5Repair harness short at identified location
- 6Confirm CMP signal activity while cranking after repair
- 7Evaluate tone wheel and mechanical issues only after clean signals are confirmed
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
5 steps locked- 1Disconnect CMP sensor connector
- 2Check signal wire for short to ground with sensor disconnected
- 3If short clears with sensor disconnected — replace CMP sensor
- 4If short persists — inspect harness at cover-edge and bracket chafe points
- 5Repair harness short at identified location
- 6Confirm CMP signal activity while cranking after repair
- 7Evaluate tone wheel and mechanical issues only after clean signals are confirmed
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
SPN 723 FMI 4 requires short isolation before any gear-train or mechanical timing conclusions. CMP circuit must be proven valid first.