The normal value of the ECT sensor voltage is 2V at cold engine and 0.5V at warm engine. Common problem is that the output resistance (and voltage) changes incorrectly beyond its normal range.During engine warming the voltage should decrease in accordance with the values given in Table-1.
Procedure for verification the functionality of the ECT sensor Here the voltage and the resistance are increasing with the raise of the temperature. Used in some older systems, such as Renix. With positive temperature coefficient.Their resistance decreases with the increase of the temperature. These are the most popular sensors used in cars. With negative temperature coefficient.Thereby, a coolant temperature dependent variable voltage signal is send to the onboard computer. At 90 ✬ its resistance is in the range of 200Ω to 300Ω. ECT gradually heats and its resistance reduces proportionately. After the engine start, coolant temperature begins to rise. In cold engine and an ambient temperature of 20 ✬ the sensor resistance is between 2000Ω and 3000Ω. In order to convert the ECT resistance variation to voltage variation, which is further processed by the ECU, the ECT sensor is connected in a circuit typically supplied with a reference voltage of +5V. The onboard computer uses the signal of ECT as the main correction factor when calculating the ignition advance and the injection duration. It is a two-wire thermistor immersed in coolant and measures its temperature. The engine coolant temperature sensor is temperature-variable resistor, which usually has a negative temperature coefficient.