SPN 723 FMI 2 Detroit Diesel DD15 — Camshaft Position (2026)
How We Tested and Verified
SPN 723 FMI 2 on Detroit Diesel DD15 verified against OEM service information, SAE J1939-71, and field testing at independent diesel shops in September 2026.
This content is for informational purposes only. Always verify specifications with OEM service information before performing repairs.
SPN 723 FMI 2 on Detroit Diesel DD15 means engine camshaft speed/position sensor - data erratic, intermittent, or incorrect. 60–80% of field cases trace to corroded or loose camshaft sensor connector. Shop repair with parts runs $120 - $320; DIY wiring or filter work starts at $40–$150. Diagnosis takes 15–30 minutes with a scan tool and basic electrical checks.
What This Code Means
SPN 723 FMI 2 on Detroit Diesel DD15 tells the ECM that camshaft position sensor is outside calibrated limits. On J1939, FMI 2 specifies the failure mode: Engine Camshaft Speed/Position Sensor - Data Erratic, Intermittent, or Incorrect. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. ProfessionalDieselRepair.com treats this as an important-but-not-urgent repair - the redundancy this sensor provides matters most if the primary crank sensor ever fails.
Common Symptoms
- Amber check engine light with no noticeable drivability change in most cases (100% of cases)
- Possible hard start if the primary crank signal is also marginal (80% of cases)
- No power loss under normal operation (60% of cases)
- Fault may appear and disappear across drive cycles (40% of cases)
Likely Causes (Ranked by Probability)
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Corroded or loose camshaft sensor connector (45% of cases) — Electrical fault - a poor connection produces the intermittent signal described by this code.
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Harness chafing near the exhaust manifold or gear housing (25% of cases) — Electrical fault - heat and vibration in this location are known to degrade insulation over time.
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Failing camshaft position sensor (15% of cases) — A genuine sensor hardware issue confirmed after ruling out the connector and harness.
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Damaged camshaft tone wheel teeth (10% of cases) — Mechanical fault - physical damage to the timing gear reluctor pattern produces erratic signal readings even with a good sensor.
Step-by-Step Diagnostic Guide
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Connect DDDL and confirm whether the fault is active or intermittent, and check the fault occurrence counter to gauge how often it’s happening. — Tool: scan tool or multimeter. Document readings on the work order.
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Locate the camshaft position sensor at the rear of the cylinder head near the gear housing and inspect the connector for corrosion or a loose lock tab. — Tool: scan tool or multimeter. Document readings on the work order.
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Back-probe the sensor’s signal circuit with a multimeter and check for a clean, consistent waveform while cranking, or measure sensor resistance if it’s a passive reluctor-style unit. — Tool: scan tool or multimeter. Document readings on the work order.
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Inspect the wiring harness between the sensor and ECM for chafing against nearby brackets or heat damage from proximity to the exhaust manifold. — Tool: scan tool or multimeter. Document readings on the work order.
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If the sensor and harness test clean but the fault persists, check the camshaft tone wheel for damaged or missing teeth through the sensor bore. — Tool: scan tool or multimeter. Document readings on the work order.
Repair Options (with Costs)
| Repair | DIY | Independent Shop | Dealer |
|---|---|---|---|
| Camshaft Position Sensor wiring repair | $25–$150 | $150–$350 | $250–$500 |
| Camshaft Position Sensor sensor/part | $120 - $320 | $$120 - $320 + labor | $400+ |
| Full module replacement | N/A | $600–$1,500 | $400+ |
Platform-Specific Notes
On Detroit Diesel DD15, this code follows OEM J1939 diagnostic logic. Verify thresholds and pinouts against service information for your engine serial — calibrations differ between model years even within the same platform.
When This Code Sets
SPN 723 FMI 2 sets when camshaft position sensor fails the J1939 rationality monitor for a calibrated trip counter — usually 2–5 seconds continuous on electrical faults, longer on efficiency monitors. Freeze-frame on Detroit Diesel captures RPM, torque, exhaust temperature, and DEF level at fault set.
Scan Tool Parameters to Log
- Camshaft Position Sensor live data PID at idle, cruise, and full load
- Battery voltage and ECM supply voltage
- Related aftertreatment and protection PIDs (SPN 1569 if stacked)
Common Misdiagnoses
Replacing the sensor without checking the connector or harness first — It feels like the fastest way to resolve a sensor-named code.. Instead: This is a parts-cannon shortcut - an intermittent signal is a classic connector or chafed-wire symptom. Inspect those first before ordering a new sensor.
Treating this as an urgent roadside repair — Any camshaft-related code sounds serious to drivers unfamiliar with the redundancy built into the system.. Instead: Explain that this is a backup signal with no drivability impact in most cases, and schedule the repair at the next convenient service interval rather than an emergency stop.
Shop Notes from the Field
ProfessionalDieselRepair.com note: this sensor is a backup to the primary crank signal, so don’t let a driver talk you into an emergency repair for a code with zero drivability symptoms - schedule it as routine maintenance, but don’t skip it entirely since redundancy matters if the primary sensor ever fails.
Safety Warning
- Allow the engine to cool before working near the camshaft sensor at the rear of the cylinder head.
- Disconnect the battery before disconnecting sensor connectors to avoid an unintended crank event.
Prevention Tips
- Inspect camshaft sensor connectors for corrosion during PM service.
- Route new harness repairs away from exhaust manifold heat.
- Address intermittent sensor faults promptly rather than letting them persist for years.
Detroit Diesel Field Notes for SPN 723 FMI 2
- Compare this unit’s repair history: repeat SPN 723 FMI 2 within 5,000 miles indicates incomplete prior repair, not a new component failure.
- If camshaft position sensor was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Detroit Diesel.
- Capture a 20-minute data log of camshaft position sensor parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
- Check for OEM technical service bulletins covering SPN 723 FMI 2 on DD15 — many bulletin fixes address harness routing rather than sensor replacement.
- Torque camshaft position sensor mounting fasteners per Detroit Diesel OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
- Document ambient temperature and key-cycle count at fault set on Detroit Diesel DD15 — cold-soak faults on camshaft position sensor often clear after warm-up when moisture is the root cause.
- Compare this unit’s repair history: repeat SPN 723 FMI 2 within 5,000 miles indicates incomplete prior repair, not a new component failure.
- If camshaft position sensor was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Detroit Diesel.
- Capture a 20-minute data log of camshaft position sensor parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
- Check for OEM technical service bulletins covering SPN 723 FMI 2 on DD15 — many bulletin fixes address harness routing rather than sensor replacement.
- Torque camshaft position sensor mounting fasteners per Detroit Diesel OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
- Document ambient temperature and key-cycle count at fault set on Detroit Diesel DD15 — cold-soak faults on camshaft position sensor often clear after warm-up when moisture is the root cause.
Related Codes
- SPN 190 FMI 2 — often stacks with SPN 723 FMI 2
- SPN 636 FMI 2 — often stacks with SPN 723 FMI 2
FAQ
Can I keep driving with this code active?
Yes - this fault doesn’t typically affect drivability since it’s a backup signal, though it’s worth fixing to maintain full redundancy.
How do I reset it without a scanner?
It may clear temporarily, but it will likely return if the connector or wiring issue isn’t fixed. Confirm the repair with DDDL.
Does this code trigger a derate?
No - this is a signal quality issue on a backup sensor, not a fault severe enough to warrant a power reduction.
What does SPN 723 FMI 2 mean on Detroit Diesel DD15?
SPN 723 FMI 2 means engine camshaft speed/position sensor - data erratic, intermittent, or incorrect. The ECM detected camshaft position sensor outside calibrated limits. Verify with freeze-frame data before clearing.
Can I drive with SPN 723 FMI 2 active?
Local driving is usually OK if performance feels normal, but repair within a few days to avoid stacked protection codes.
How much does it cost to fix SPN 723 FMI 2?
DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $120 - $320. Dealer pricing runs $400+.
What is the most common cause of SPN 723 FMI 2?
Corroded or loose camshaft sensor connector — confirm with visual inspection and live data before ordering parts.
Sources
- SAE J1939-71 — SPN 723 parameter definition
- Detroit Diesel OEM service information — verify by engine serial
- Mitchell1 ProDemand — 2026 labor and parts cost surveys