SPN 110 FMI 0 — Engine Coolant Temperature — Too High
Engine coolant temperature is above the high limit. Sustained overheating warps heads and damages the engine, so the ECM warns and will derate; treat it as stop-now once confirmed on the gauge.
Your SPN/FMI rides along, so nearby mechanics see the fault before they quote you.
How serious is it?
Serious. Stop as soon as it's safe.
Most likely causes
- Low coolant level or a leak (hose, radiator, water pump, EGR cooler)
- Stuck thermostat or failed water pump
- Plugged radiator/CAC fins, debris, or a failed cooling fan/clutch
- Coolant-temp sensor fault reading high (verify before assuming)
First moves (roadside)
- Reduce load and get to a safe stop; idling briefly can help, but don't keep climbing a grade hot.
- Once cooled, check coolant level (NEVER open a hot pressurized cap) and look for leaks/steam.
- Inspect the fan engagement and the radiator/CAC face for bugs, mud, or debris blocking airflow.
- Compare gauge to actual — a sensor fault can read high, but confirm before continuing.
Common misdiagnoses
- Adding coolant and driving on without finding the leak or stuck thermostat.
- Blaming the sensor while the fan clutch isn't engaging.
- Overlooking a packed radiator/charge-air-cooler face as the airflow restriction.
FAQ
Engine coolant temperature is above the high limit. Sustained overheating warps heads and damages the engine, so the ECM warns and will derate; treat it as stop-now once confirmed on the gauge.
Serious — Stop as soon as it's safe.
The most common cause is: Low coolant level or a leak (hose, radiator, water pump, EGR cooler). Other possibilities include Stuck thermostat or failed water pump; Plugged radiator/CAC fins, debris, or a failed cooling fan/clutch; Coolant-temp sensor fault reading high (verify before assuming).
Stop as soon as it's safe. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Find a mechanic or related guides
General diagnostic guidance for heavy-duty diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack). Not a substitute for a scan-tool diagnosis on your specific truck.