The Engine Coolant Temperature sensor is a variable resistor, which measures the temperature of the engine coolant. The ECT sensor has a signal circuit and a low reference circuit. The powertrain control module PCM supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit.
- Inspect coolant temp sensor, connector and wiring.
- Scan for any related codes.
- Record Diagnostic Trouble Code and review diagnostics chart for appropriate test.
- Verify repair and reset trouble code.