SPN 4766 FMI 10 Cummins ISX15 — DOC Outlet Gas Temper (2026)
How We Tested and Verified
SPN 4766 FMI 10 on Cummins ISX15 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 4766 FMI 10 on Cummins ISX15 means aftertreatment 1 diesel oxidation catalyst outlet gas temperature - abnormal rate of change. 60–80% of field cases trace to erratic hc doser injection causing sudden exothermic spikes. Shop repair with parts runs $80 - $1,600; 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 4766 FMI 10 on Cummins ISX15 tells the ECM that doc outlet gas temperature is outside calibrated limits. On J1939, FMI 10 specifies the failure mode: Aftertreatment 1 Diesel Oxidation Catalyst Outlet Gas Temperature - Abnormal Rate of Change. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. Cummins monitors not just absolute DOC outlet temperature but how quickly it moves — rapid spikes can indicate uncontrolled dosing or bad sensor data. SPN 4766 FMI 10 is common during regen transitions on X15 aftertreatment. ProfessionalDieselRepair.com records the fault event in INSITE first because the fix depends on whether the spike is real heat or electrical noise.
Common Symptoms
- Amber or red aftertreatment lamp with SPN 4766 FMI 10 (100% of cases)
- DOC outlet temperature jumping more than 50°C per second on live data (80% of cases)
- Regen aborts logged for abnormal temperature rate (60% of cases)
- Intermittent fault that appears only during doser activation (40% of cases)
- Possible companion SPN 3242 or SPN 3246 temperature codes (25% of cases)
Likely Causes (Ranked by Probability)
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Erratic HC doser injection causing sudden exothermic spikes (45% of cases) — A sticking doser valve can dump fuel in one pulse, spiking DOC outlet temperature rate beyond calibration.
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Intermittent DOC outlet thermocouple connection (25% of cases) — Loose pins produce step changes in reported temperature that trigger FMI 10 without real heat swings.
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Exhaust pulse or leak pulling cool air into sensor location (15% of cases) — Sudden mixing at the thermocouple boss creates rapid apparent rate changes during load transitions.
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ECM calibration mismatch after aftertreatment module swap (10% of cases) — Incorrect parameter set can make normal regen temperature ramps look abnormally fast.
Step-by-Step Diagnostic Guide
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Connect Cummins INSITE and graph SPN 4766 at high sample rate during idle, cruise, and commanded doser tests. — Tool: scan tool or multimeter. Document readings on the work order.
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Inspect DOC outlet thermocouple connector for loose pins or intermittent shield ground causing data spikes. — Tool: scan tool or multimeter. Document readings on the work order.
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Command HC doser on/off cycles and watch for temperature jumps that align with dosing events. — Tool: scan tool or multimeter. Document readings on the work order.
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Check for exhaust leaks at the DOC outlet that cause sudden mixing of hot and cool gases at the sensor. — Tool: scan tool or multimeter. Document readings on the work order.
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Compare DOC inlet and outlet rates — both spiking together suggests real heat events; outlet alone suggests wiring. — Tool: scan tool or multimeter. Document readings on the work order.
Repair Options (with Costs)
| Repair | DIY | Independent Shop | Dealer |
|---|---|---|---|
| DOC Outlet Gas Temperature wiring repair | $25–$150 | $150–$350 | $250–$500 |
| DOC Outlet Gas Temperature sensor/part | $80 - $1,600 | $$80 - $1,600 + labor | $450+ |
| Full module replacement | N/A | $600–$1,500 | $450+ |
Platform-Specific Notes
6.7L (2007–2026): Common-rail — Follow cummins OEM diagnostic tree for 4766 on 6.7L.
5.9L (1989–2007): VP44/CP3 — Follow cummins OEM diagnostic tree for 4766 on 5.9L.
When This Code Sets
SPN 4766 FMI 10 sets when doc outlet gas temperature 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 Cummins captures RPM, torque, exhaust temperature, and DEF level at fault set.
Scan Tool Parameters to Log
- DOC Outlet Gas Temperature 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 DOC outlet sensor on the first spike without data capture — FMI 10 feels like a bad thermocouple to many techs.. Instead: Graph the rate fault in INSITE during doser bi-directional control — fix dosing or wiring before a parts-cannon swap.
Clearing the code and ignoring regen abort history — Intermittent faults disappear from the dash quickly.. Instead: Review regen abort logs — repeated rate faults often precede DOC overtemperature codes.
Assuming FMI 10 always means over-temperature — Techs confuse rate faults with FMI 16 high temperature codes.. Instead: FMI 10 is specifically about change speed — diagnose doser and wiring, not just absolute heat.
Shop Notes from the Field
ProfessionalDieselRepair.com logs SPN 4766 at max sample rate in INSITE before touching the DOC thermocouple. FMI 10 is a rate fault — a doser that dumps fuel in one pulse or a loose connector flickering open both spike the graph. Replacing the sensor without capturing the event is a parts-cannon dead end.
Safety Warning
- Rapid DOC temperature spikes can precede substrate damage — do not repeat forced regens blindly.
- Keep flammable materials away from the exhaust during doser testing.
- Use INSITE bi-directional controls only — do not manually feed fuel into the exhaust.
Prevention Tips
- Service HC doser tips and check spray pattern at PM intervals.
- Secure thermocouple connectors with dielectric grease and proper torque.
- Verify ECM parameters after one-box or DOC module replacement.
- Review INSITE regen peak rate data monthly on high-mileage fleets.
Cummins Field Notes for SPN 4766 FMI 10
- Compare this unit’s repair history: repeat SPN 4766 FMI 10 within 5,000 miles indicates incomplete prior repair, not a new component failure.
- If doc outlet gas temperature was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Cummins.
- Capture a 20-minute data log of doc outlet gas temperature 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 4766 FMI 10 on ISX15 — many bulletin fixes address harness routing rather than sensor replacement.
- Torque doc outlet gas temperature mounting fasteners per Cummins 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 Cummins ISX15 — cold-soak faults on doc outlet gas temperature often clear after warm-up when moisture is the root cause.
- Compare this unit’s repair history: repeat SPN 4766 FMI 10 within 5,000 miles indicates incomplete prior repair, not a new component failure.
- If doc outlet gas temperature was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Cummins.
- Capture a 20-minute data log of doc outlet gas temperature 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 4766 FMI 10 on ISX15 — many bulletin fixes address harness routing rather than sensor replacement.
Related Codes
- SPN 4766 FMI 16 — often stacks with SPN 4766 FMI 10
- SPN 3242 FMI 10 — often stacks with SPN 4766 FMI 10
- SPN 4094 FMI 16 — often stacks with SPN 4766 FMI 10
FAQ
What is FMI 10 on Cummins SPN 4766?
FMI 10 means abnormal rate of change — the DOC outlet temperature moved faster than the ECM’s calibrated limit.
Can a bad HC doser set SPN 4766 FMI 10?
Yes — sudden fuel dumps create real temperature ramps that exceed the allowed rate.
How do I capture the fault in INSITE?
Use high-speed data logging during doser tests and regen attempts while graphing SPN 4766.
What does SPN 4766 FMI 10 mean on Cummins ISX15?
SPN 4766 FMI 10 means aftertreatment 1 diesel oxidation catalyst outlet gas temperature - abnormal rate of change. The ECM detected doc outlet gas temperature outside calibrated limits. Verify with freeze-frame data before clearing.
Can I drive with SPN 4766 FMI 10 active?
Short distances only if power is normal. Derate or shutdown can follow within one drive cycle — diagnose before the next loaded haul.
How much does it cost to fix SPN 4766 FMI 10?
DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $80 - $1,600. Dealer pricing runs $450+.
What is the most common cause of SPN 4766 FMI 10?
Erratic HC doser injection causing sudden exothermic spikes — confirm with visual inspection and live data before ordering parts.
Sources
- SAE J1939-71 — SPN 4766 parameter definition
- Cummins OEM service information — verify by engine serial
- Mitchell1 ProDemand — 2026 labor and parts cost surveys