DTC P0118-00: Engine Coolant Temperature Circuit High Input: General Description

The Engine Coolant Temperature Sensor (ECTS) measures the temperature of engine coolant. The ECTS is located near the thermostat housing of the cylinder head. The ECTS is a thermistor (A Variable Resistor that changes along with ECT) in series with a fixed resistor in the ECM. The ECM applies 5V to the ECTS. The ECM monitors the voltage across the ECTS and converts it into a temperature reading. When the engine is cold the ECTS resistance is high, and when the engine is warm the ECTS resistance is low. Therefore, when the engine is cold the ECM will receive a high voltage input, and when the engine is warm the ECM will receive a low voltage input. The signal from the ECTS is used for Injection control, ignition timing, idle speed and cooling fan control.