SPN 723 FMI 3 — Camshaft Speed / Position Circuit Voltage Above Normal
CMP high-voltage codes are open-circuit diagnostics before mechanical timing work. Timing teardown performed for an open CMP circuit is the most documented misdiagnosis.
Fault Overview
SPN 723 FMI 3 indicates the camshaft speed or position sensor circuit voltage is above the valid maximum — an open circuit or high-signal class fault. Open signal wire, failed CMP sensor, unplugged connector after gear-train service, damaged harness, and poor reference or ground are the primary causes.
Engine & Platform Coverage
Possible Causes
- 1.Open signal wire from damage near front cover or gear housing
- 2.Failed CMP sensor with internal open element
- 3.Unplugged connector after gear-train or front cover service
- 4.Damaged harness at front cover or gear housing
- 5.Poor reference or ground at CMP sensor connector
Wiring & Circuit Notes
Inspect the CMP connector at the front cover or gear housing for chafe and oil contamination. Confirm connector is fully locked after any recent gear-train service. Verify reference and ground at the sensor connector.
DVOM Specs & Sensor Tests
Confirm CKP signal is present while cranking — CKP present with CMP absent often supports CMP circuit or sensor fault rather than mechanical timing. Verify reference and ground at CMP sensor connector. Check signal wire continuity from sensor to ECM. Replace CMP sensor after circuit is proven. Evaluate mechanical timing only after clean signals are confirmed.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Confirm CKP signal is present while cranking
- 2Inspect CMP connector lock — confirm fully seated after any recent gear-train service
- 3Verify reference and ground at CMP sensor connector
- 4Check signal wire continuity from sensor to ECM
- 5Replace CMP sensor after circuit is proven
- 6Evaluate mechanical timing only after clean signals are confirmed
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
4 steps locked- 1Confirm CKP signal is present while cranking
- 2Inspect CMP connector lock — confirm fully seated after any recent gear-train service
- 3Verify reference and ground at CMP sensor connector
- 4Check signal wire continuity from sensor to ECM
- 5Replace CMP sensor after circuit is proven
- 6Evaluate mechanical timing 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
AI Diesel Tech walks you through every evidence gate in the correct order. Choose the plan that fits your shop.
Related Resources
Related Systems
Related Fault Codes
Related Sensor Locations
Common Symptoms
Related Articles
AI Diesel Tech — The Technician's Diagnostic Engine
AI Diesel Tech diagnostic logic is built by an ASE Certified Diesel Technician and engineered for professional shop use. Trusted by technicians nationwide — used in shops, fleets, and training programs.
Summary
SPN 723 FMI 3 is an open-circuit CMP diagnosis. CKP confirmation and circuit proof are required before any mechanical timing conclusions.