A variety of sensors provide information to the ECM/PCM regarding engine operating characteristics. These sensors and their functions are described below. Be sure to take note that not every sensor described is used with every engine application.
Coolant Temperature (ECT)
The Engine Coolant Temperature Sensor (ECT) is a thermister (a resistor which changes value based on temperature) mounted on the engine coolant stream. As the temperature of the engine coolant changes, the resistance of the coolant sensor changes. Low coolant temperature produces a high resistance (100,000 ohms at 40°C/40°F), while high temperature causes low resistance (70 ohms at 130°C/266°F).
The ECM/PCM supplies a 5 volt signal to the coolant sensor and measures the voltage that returns. By measuring the voltage change, the ECM/PCM determines the engine coolant temperature. The voltage will be high when the engine is cold and low when the engine is hot. This information is used to control fuel management, IAC, spark timing, EGR, canister purge and other engine operating conditions.
A failure in the coolant sensor circuit should either set a Code 14 or 15. These codes indicate a failure in the coolant temperature sensor circuit.
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It looks like the above, under hood, passenger side, upper engine area, mounted in front side of water outlet (according to Autozone.com).
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