Detroit SPN 110 FMI 0 �?Engine Coolant Temperature High Severity

Code Details

Plain-English Meaning

Detroit DD13 and DD15 engines monitor coolant temperature and actively protect themselves when it climbs out of the normal range. FMI 0 is the most serious above-normal level �?not a warning that the temperature is trending up, but a signal that it has already exceeded the safe limit. The protection system reduces power and warns the driver. Continuing to operate a severely overheating engine risks head gasket failure, cylinder head distortion, or internal damage that is considerably more expensive than the original cooling fault.

SPN 110 is Engine Coolant Temperature 1 in J1939. FMI 0 means the measured value is valid and above the upper limit of the normal operating range at the highest severity level. On Detroit DD13/DD15 engines, the MCM2.2 monitors a coolant temperature thermistor (NTC type) mounted in the cooling circuit. A genuine overtemperature condition sets FMI 0; a sensor failure would typically produce FMI 3 (shorted to supply) or FMI 4 (shorted to ground or open). The engine protection module links coolant temperature to derate thresholds and may progressively reduce torque as temperature increases further.

Common Symptoms

• Red stop lamp or amber warning lamp active on the dash
• Engine protection derate �?noticeably reduced power or speed limitation
• Coolant temperature gauge reading in the danger zone
• Steam or coolant smell from under the hood in severe cases
• Engine may enter a protection shutdown sequence if temperature continues to rise

Possible Causes

Possible causes may include the items below. The list is not a parts diagnosis.

• Coolant loss from an external leak: failed hose, water pump seal, head gasket, or radiator
• Thermostat stuck closed, preventing hot coolant from circulating through the radiator
• Fan clutch slipping or not engaging, reducing airflow through the radiator at low road speeds
• Radiator core clogged with scale, road debris, bugs, or internal scaling reducing heat rejection
• Water pump impeller slipping or cavitating, reducing coolant flow rate through the circuit
• High ambient temperature combined with sustained grade climbing or loaded operation exceeding cooling capacity

First Checks

• Allow the engine to cool before opening the radiator or overflow tank �?never open a hot pressurized cooling system
• Check coolant level in the overflow reservoir; a low level points to a leak somewhere in the system
• Inspect hose connections, the water pump area, and the front of the radiator for coolant residue, wet spots, or dried deposits
• Confirm the fan engages when the engine is at operating temperature; a fan clutch that slips or disengages is a common cause in vocational and construction duty cycles
• Connect Detroit DiagnosticLink and view live coolant temperature alongside fan command status and any related protection-event history

Can I Keep Driving?

Stop the vehicle safely when a red stop lamp is active or when this code is present with a significant power reduction. Do not restart until the cause is identified �?a brief cooldown does not fix the underlying fault and the engine can overheat again quickly after restart.

Related Lookup Pages

• SPN 110 topic page
• FMI 0 explanation
• Detroit Diesel manufacturer hub
• Search this code