FC 2963 — Engine Coolant Temperature – Above Normal, Least Severe (SPN 110 FMI 15) — Cummins ISX15

Diagnostic reference for Cummins ISX15 (2010–2017) ECM CM2250/CM2350.

Updated October 15, 2026

What it means

Engine coolant temperature is above the engine protection warning level. On Cummins ISX15 (2010–2017) this is SPN 110 FMI 15, mapped as FC 2963. The code is least severe; it indicates the ECM has seen coolant temperature high enough to warrant a warning but not an immediate shutdown. Typical on this platform: low coolant, a stuck thermostat, a fan or radiator problem, or heavy load in hot weather.¹

Most likely causes

1. Low engine coolant level or air in the cooling system — Reduced coolant volume lowers heat transfer and can cause localized overheating. Check the sight glass/level in the surge tank with the engine cold and verify no external leaks at hoses, water pump weep hole, radiator, EGR cooler connections, and the oil cooler. Inspect for signs of coolant loss and for combustion gas in the coolant.¹
2. Thermostat stuck closed or opening late — Restricted coolant flow through the engine raises temperature under load. With the engine at operating temperature, monitor coolant temperature rise rate and compare to expected warm-up profile using an INSITE scan tool. A slow rise or temperature that climbs quickly under light load suggests a thermostat issue.¹
3. Cooling fan or fan clutch not providing adequate airflow — Insufficient airflow at idle or low road speed reduces radiator heat rejection. Observe fan engagement commanded by the ECM versus actual fan speed/engagement. Check for debris blocking the radiator/charge-air cooler stack and verify proper airflow through the core.¹
4. Radiator or charge-air cooler blockage / external restriction — External debris, bent fins, or internal scaling reduces heat transfer. Inspect the radiator and CAC for blockage between cores, check for uniform temperature across the radiator face with a non-contact thermometer after a loaded run, and confirm coolant flow is not restricted.¹
5. Heavy load and high ambient temperature operation — Sustained high load in hot weather can push coolant temperature toward the warning threshold even with a healthy cooling system. Correlate occurrence with ambient conditions, grade, and load. If temperature normalizes under lighter load or cooler ambient, system capacity may be marginal.¹

How to diagnose

1. Verify active vs inactive status and freeze-frame data. Use INSITE to confirm FC 2963 is active, note engine speed, load, vehicle speed, ambient temperature, and coolant temperature at set.
2. Check coolant level cold and hot. Inspect for external leaks, proper surge tank cap seal, and signs of coolant loss. Look for oil in coolant or coolant in oil as indicators of internal issues.
3. Review recent operating conditions. Confirm if the event occurs under specific load/ambient conditions or is persistent across all operation.
4. Monitor live coolant temperature and fan control. Compare commanded fan state/speed to actual engagement and observe temperature response during a controlled load increase.
5. Inspect radiator/charge-air cooler stack for external blockage and verify airflow. Check for debris, bent fins, and proper shroud sealing.
6. Assess thermostat function via warm-up profile and stabilized temperature at idle and under load using scan data. Compare to expected temperature range for ISX15.
7. Check coolant quality and condition. Verify proper coolant type/concentration and absence of contamination that reduces heat transfer.
8. If temperature remains high with adequate coolant level and airflow, investigate coolant flow restrictions such as a restricted radiator, water pump performance, or EGR cooler flow issues using temperature mapping and flow tests as appropriate.
9. Clear codes after corrections and perform a road test under load to confirm coolant temperature stays within normal range and FC 2963 does not reset.

Common mistake to avoid

Replacing the EGR valve without testing it. If the valve still moves freely, a carbon cleaning often fixes the flow code; and if it opens on command but the code stays, the blockage is in the passages or cooler, not the valve. Source: FleetRabbit — EGR valve problems and repair.

Parts and tools you may need

• INSITE diagnostic software with Cummins ISX15 adapter
• Non-contact infrared thermometer
• Coolant test strips/refractometer
• Basic hand tools for inspection covers and hose clamps

Tools you’ll need

• diagnostic scan tool with Cummins INSITE capability — Read FC 2963/SPN 110 FMI 15 status, freeze-frame data, and live coolant temperature plus fan command to confirm the over-temperature event.
• infrared thermometer — Map radiator, thermostat housing, and hose temperatures to find hot/cold spots indicating a stuck thermostat or flow restriction.
• coolant system pressure tester — Verify surge tank cap seal and detect external leaks that cause low coolant and high temperature warnings.
• digital multimeter — Check engine coolant temperature sensor resistance/voltage to rule out a sensor reading error versus actual overheating.

Rough cost and difficulty

Typical US independent-shop figures; labor runs about $140–$200 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If coolant temperature continues to rise into the severe range, if there are signs of head gasket failure, or if the code is accompanied by engine protection derates, stop operation and have the vehicle inspected by a qualified diesel technician. Do not attempt repairs on high-pressure fuel systems. On ISX15, SCR-related derates (e.g., FC 3712/3714) are effects of underlying faults and must be diagnosed separately. This guide is for diagnosis only. Safety-critical repairs require trained personnel and proper procedures.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources