The engine coolant temperature sensor provides an input to the powertrain control module (PCM). As coolant temperature varies, the engine coolant temperature sensor resistance changes, resulting in a variable input voltage to the PCM. When the engine is cold, the PCM will demand slightly richer air-fuel mixtures and higher idle speeds until normal operating temperatures are reached. The engine coolant sensor input also determines operation of the radiator fan.
Low coolant level can cause erratic ECT performance.
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.