Diagnostic Overview
Detroit SPN 110 FMI 16 generally indicates engine coolant temperature is above normal at a moderate severity level. This is more urgent than FMI 15 and may lead to torque reduction or shutdown logic if the temperature continues rising. It usually points to a real cooling-system problem unless sensor data proves otherwise.
Likely Causes
Cooling system restriction, low coolant, fan not engaging, thermostat failure, radiator airflow restriction, coolant pump problem, heavy load overheating, or coolant temperature sensor error.
What To Check First
Confirm actual temperature with a known-good reading, inspect coolant level and fan operation, check for radiator restriction, verify thermostat and coolant flow, and repair before the fault escalates. Verify final definition in Detroit DiagnosticLink because FMI meaning can vary by engine year, ACM/MCM calibration, and emissions level.