SPN 110: coolant temperature - when to stop
Updated: 2026-11-10
In short. With FMI 0, 15 and 16 treat the overheating as real: stop at the first safe opportunity and let the engine cool. FMI 3 and 4 point to the sensor circuit, but until the temperature is checked with a second thermometer, assume the overheating is real.
FMI breakdown
SPN 110 in J1939 is Engine coolant temperature.
| FMI | Meaning | What to do |
|---|---|---|
| 0 | Above normal, most severe level (Cummins ISB 6.7: FC 151) | Stop, let it cool |
| 16 | Above normal, medium urgency (Cummins FC 146) | Do not drive, find the cause |
| 15 | Above normal, low urgency (Cummins FC 2963) | Do not drive, find the cause |
| 3 | Sensor circuit voltage above normal or short to positive (Cummins FC 144) | Check connector and wiring |
| 4 | Sensor circuit voltage below normal or short to ground (Cummins FC 145) | Check connector and wiring |
Temperature thresholds and the unit's reaction (warning, derate, shutdown) differ between manufacturers: check the manual for your engine.
Can you drive
No. The time reserve in overheating is measured in minutes, and pushing on "to the nearest place" quickly destroys the cylinder head and gasket. With FMI 3 and 4 first check whether the sensor is lying.
Order of actions
- Stop and let the engine cool.
- Do not open the expansion tank cap on a hot engine: the liquid under pressure is thrown out as steam.
- When cooled, check the coolant level, the fan belt and clutch, and radiator dirt.
- Compare the dashboard with an infrared thermometer on the upper radiator hose: a match means the overheating is real.
- No match: inspect the sensor connector and wiring; a break gives a falsely high voltage, a short gives a false overheat.
When to see a workshop
- temperature really is high with a normal coolant level: a faulty thermostat, pump, fan clutch or an air lock after a coolant change are possible;
- FMI 3 or 4 repeats after the connector and wiring were checked: diagnostics of the sensor and its circuit.
Questions and answers
Can I drive with SPN 110 FMI 0?
No. Stop at the first safe opportunity and let the engine cool.
Can I open the expansion tank cap?
Not on a hot engine: the liquid under pressure is thrown out as steam.
How do I tell real overheating from a sensor fault?
Compare the dashboard with an infrared thermometer on the upper radiator hose. If they match, the overheating is real.
What do FMI 3 and 4 mean?
The sensor circuit: voltage above normal or short to positive (3), below normal or to ground (4). It is not proof that the engine is overheated.
Code pages on the site
- SPN 110 - coolant temperature
- SPN 111 - coolant level
- Overheating uphill
- SPN 100 - oil pressure
Checked against manufacturer manuals and tables; the same facts as in our videos and articles. The decision to drive remains with the driver.
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