The thermostat could be stuck closed
the fan is bad
the fan relay is bad
check for power at the fan when the engine is at the operating temperature.
the fan relay is going bad all the time, it a solid state relay below the power train control module. it's on left frame rail

Your thermostat is closing replace with new one and that should fix the proble you can fet one at any auto parts store

Your fan may not be coming on. check your fuses maybe you blew one or the fan went bad all together