SPN 723 FMI 2 — Camshaft Speed / Position Data Erratic
SPN 723 FMI 2 means the cam sensor signal is erratic or inconsistently correlates with the expected pattern. This is a classic heat-and-harness diagnosis — hot intermittent no-starts and stalls after recent front cover or valve-cover service are the most common presentations.
Fault Overview
FMI 2 is the erratic or data-valid-but-intermittent class on the cam sensor circuit. The ECM monitors cam signal pattern and correlation with the crank sensor — an erratic signal that does not match the expected pattern sets FMI 2. Failing cam sensor, damaged reluctor or tone features, harness intermittents, connector oil intrusion, and improper air gap are the primary causes. Heat-soak no-starts and intermittent faults after recent front cover or valve-cover service are documented patterns. Suspecting the ECM before proving sensor and harness integrity is the most common wasted-time path on this fault.
Engine & Platform Coverage
Symptoms
- •Cam sensor erratic fault active
- •Intermittent no-start
- •Stall when hot
- •Cam-crank correlation intermittent
- •Hard start after heat soak
- •Intermittent injector disable from sync loss
Possible Causes
- 1.Failing cam sensor — internal failure under heat
- 2.Damaged reluctor or tone features — physical damage to target
- 3.Harness intermittents — flex point damage near valve cover or gear housing
- 4.Connector oil intrusion — oil migration into sensor connector body
- 5.Improper air gap — sensor too far from target after service
- 6.Recent front cover or valve-cover service — disturbed sensor or harness
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 — Visual Connector and Oil Intrusion Inspection: Inspect the cam sensor connector for oil intrusion, corrosion, and pin damage. Inspect the sensor pigtail at the valve cover and gear housing for chafe points and moisture. Oil intrusion into the sensor connector body is a documented cause of erratic signal behavior.
- 2Binary Decision Gate — Scope or PID Pattern Analysis: Capture cam sensor signal pattern with a scope or monitor cam signal PIDs while cranking or running. Look for dropouts, amplitude variations, and pattern inconsistencies. An erratic pattern with good connector condition points to sensor failure or target damage.
- 3Override Manager — Air Gap and Tone Inspection: Verify sensor air gap per OEM specification. Inspect the reluctor or tone ring for damaged features. A sensor reinstalled too far from the target after front cover service produces erratic signals without any sensor failure.
- 4Safety Interceptor — Hot Harness Wiggle Test: Perform a harness wiggle test at operating temperature. Intermittent faults that only appear when hot are often caused by harness flex point damage that opens under thermal expansion. Wiggle the harness at the valve cover and gear housing while monitoring cam signal PIDs.
- 5Resume Point — Recent Service Assessment: If the fault appeared after recent front cover or valve-cover service, assess for disturbed sensor mounting, incorrect air gap, or harness damage from the service. Service-induced cam sensor faults are a documented pattern.
- 6Verification Loop — Post-Repair Signal Confirmation: After repair, verify cam signal pattern is stable during cranking and at operating temperature. Confirm cam-crank correlation is within OEM specification.
- 7Repair Ledger Output — Sensor or Harness Decision: Replace sensor after connector, air gap, and harness integrity are proven good. Repair harness if flex point damage is found. Repair tone ring or target if physical damage is confirmed.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
3 steps locked- 1Repair connector oil intrusion or corrosion.
- 2Repair harness flex point damage found by hot wiggle test.
- 3Correct sensor air gap if out of specification after service.
- 4Replace cam sensor after connector, air gap, and harness proof.
- 5Repair or replace tone ring if physical damage is 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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Related Resources
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Summary
SPN 723 FMI 2 is a classic heat-and-harness diagnosis. The AI Diesel Tech FSM enforces the hot intermittent process to prevent unnecessary ECM suspicion on cam sensor faults.