Method and system for diagnosing lack of coolant

Disclosed are a method and a system for diagnosing the insufficiency of coolant of a car, which includes: a preparation step of checking whether the car is stopped and is on a flat ground; an operation step of applying a fixed predetermined output to a coolant water pump if the car is stopped and is on a flat ground; a measurement step of measuring the rotational velocity of a water pump impeller while the predetermined output is applied to the coolant water pump; and a determination step of determining whether the insufficiency of coolant by comparing the measured rotational velocity of the water pump impeller with a prepared reference velocity.