Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .
Circuit Description
Engine Coolant Temperature (ECT) sensor is a thermistor which changes resistance based on temperature. ECT sensor is mounted in water pump housing. ECT sensor has a signal and ground circuit. PCM applies a voltage (about 5 volts) on signal circuit to sensor and monitors changes in this voltage caused by changes in resistance of sensor to coolant temperature.
When coolant is cold, sensor resistance is high and PCM signal voltage is only pulled down a small amount through sensor ground. When coolant is warm, sensor resistance is low and PCM signal voltage is pulled down a greater amount. This causes PCM to sense a low signal voltage (high temperature). When PCM senses a signal voltage higher than normal operating range (1.5-2.0 volts), DTC will set.
DTC will set when following conditions are present
- Engine operating more than 20 seconds.
- PCM indicates engine coolant temperature more than 304°F (151°C).