For 1990-2009 cars

(1) | Switch Terminal (Brass)
(2) | Calibration Temperature
(2) | Calibration Temperature
(3) | Sender Terminal (Silver)

The engine coolant temperature switch activates a warning lamp in the instrument cluster if the engine overheats. With optional instrumentation, a temperature gage replaces the warning lamp. The temperature gage is driven with a transducer. The engine coolant temperature switch is not serviceable. If it is faulty, it should be replaced.

If the pressure in the cooling system is too low, or if the coolant does not contain enough ethylene glycol antifreeze, the coolant will boil without the TEMP indicator light coming on. Pure water could boil at 119° C (247° F) and the TEMP indicator light would not come on, even with a 103 kPa (15 psi) cooling system. Pure water also lacks the necessary rust inhibitors and water pump lubricant.