possibly the water pump
Measures the temperature of the water in your engine block, usually right where the water comes in from the radiator.
In most vehicles there are different temperature readings, especially in newer vehicles. The TEMP light usually means the Coolant temperature in the radiator. If a warning light comes on it usually means your vehicle is overheating and should be checked out by a mechanic asap.
The light is not a coolant light, it is a temperature light which comes on when the temperature of the coolant is above the limits. In other words you engine is overheating. Can be defective thermostat, bad water pump, clogged radiator, or blown head gasket.
Pull over and park when it's safe to do so and shut the engine off before any damage is done. Contact your trusted mechanic for diagnoses.
Fill your coolant to the level that it should be at. If it still comes on when the coolant is at its proper area, then it is an improper sensor. You will need to have it replaced immediately to reset the sensor.
If your engine coolant temperature gauge is indicating that it is running much cooler than normal ( it sounds like the engine cooling thermostat is sticking open / not closing completely ) which means you need to have the thermostat changed. You should consider if have good heat from your heater and if your check engine light comes on.
Sounds like you have a thermostat problem. Have it changed and have the cooling system flushed and refilled with fresh coolant. That should cure the problem.
The cooling fans on a 99 Nissan Maxima will not come on if the coolant temperature sensor is defective. The fan only comes on when the temperature passes a threshold.
because the power comes on slowly because of the temprature
Check coolant level in coolant recovery tank and radiator
I have seen this before more than likely your coolant sensor has a internal short and needs to be replaced.