Code Details
| Display code | SPN 110 FMI 0 |
|---|---|
| SPN | 110 |
| FMI | 0 |
| OEM code | None listed |
| Manufacturer | GM |
| System | Engine �?cooling system |
| Component | Engine coolant temperature sensor / cooling system |
| Source address | Unknown or not applicable |
| Severity | stop safely |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-11 |
Plain-English Meaning
The Duramax L5P cooling system keeps combustion temperatures under control. When coolant temperature rises above the warning threshold, the system is not rejecting heat fast enough. The Silverado/Sierra HD platform uses an electric cooling fan, which the ECM controls �?a fan failure or ECM fault can allow coolant to overheat under conditions that a working fan would handle. On GM Sierra 4500/5500 and Express 4500 trucks with the 6.6L L5P Duramax, the cooling system uses a belt-driven mechanical water pump with an electronically controlled thermostat on some model years. GDS2 monitors coolant temperature sensor data and fan clutch status. The L5P is a gasoline/diesel crossover platform, and some cooling system components — such as the coolant reservoir cap pressure rating — differ from traditional heavy-duty diesel engines. Verifying the correct replacement coolant concentration and reservoir cap pressure rating is part of a thorough cooling system service.
SPN 110 FMI 0 is Engine Coolant Temperature above normal in J1939. On the GM Duramax L5P, the ECM controls the electric cooling fan based on coolant temperature, A/C demand, and charge air temperature. GM scan tools (GDS2) or an OBD2 reader with enhanced parameters can monitor coolant temperature, fan duty cycle, and thermostat activity.
Common Symptoms
- Coolant temperature warning on the instrument cluster
- Possible reduced engine power if protection derate activates
- Fan running at high speed if the ECM is responding correctly to the high temperature
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Low coolant level
- Thermostat stuck closed
- Radiator blocked
- Electric cooling fan module or fan clutch failure
- Water pump impeller failure or cavitation
- EGR cooler internal leak
First Checks
- Check coolant level in the overflow reservoir
- Confirm the electric cooling fan is operating at high speed when coolant temperature is elevated
- Use a GM scan tool to monitor coolant temperature and commanded fan duty cycle
- Inspect for external coolant leaks
- Connect GDS2 and monitor coolant temperature and cooling fan speed in real time
- Check the coolant reservoir cap pressure rating and replace if below specification
Can I Keep Driving?
Reduce load and stop if temperature continues to rise. Overheating the L5P risks head gasket and other internal engine damage.
Related Codes
Related Lookup Pages
Sources
- GM Trucks Service Support — Duramax Diesel Resources General Motors LLC · oem · accessed 2026-06-11 · confidence medium
Source: General Motors LLC, GM Trucks Service Support — Duramax Diesel Resources. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium
Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
Does the GM Duramax L5P use an electric or viscous cooling fan?
The Duramax L5P in full-size HD pickups (Silverado 2500HD/3500HD and Sierra 2500HD/3500HD) uses an electric cooling fan controlled by the ECM. This is different from the viscous fan clutches used in many heavy-duty commercial trucks. If the electric fan module fails, the ECM loses its primary active cooling tool, which can lead to rapid coolant temperature increases under load.
How does the Duramax L5P cooling system differ from the LML and LGH generations?
The L5P was introduced for 2017 and features updated combustion and emissions systems. The cooling system architecture uses the same basic configuration as earlier Duramax engines but with updated thermal management strategies. The reverse-flow cooling design of the 6.7 Power Stroke is not used in the Duramax �?the L5P uses a conventional coolant flow path from the pump through the block to the heads.
Can DPF regen cycles contribute to Duramax L5P overheating?
Active DPF regen increases exhaust system temperatures and adds some heat load to the engine, but the regen contribution to coolant temperature is generally small. If coolant temperature rises significantly during a regen, it more likely reflects a borderline cooling system condition rather than the regen itself being the primary cause.