Right Hand Drive

LOCATION
The Engine Coolant Temperature (ECT) Sensor is threaded into the thermostat housing.

PURPOSE
The sensor element extends into the coolant passage where it maintains constant contact with the engine coolant. The Powertrain Control Module (PCM) uses this sensor to measure the temperature of the engine coolant.

THEORY AND OPERATION
The sensor is used to calculate injector pulse width when the engine is cold. Input from the sensor will also affect Idle Air Control (IAC) motor position, and ignition spark advance.

The sensor is a Thermistor-type sensor (Resistance varies opposite temperature). At cold temperatures, resistance is high. As temperature increases, resistance will decrease.

The engine controller sends out a reference voltage of approximately 5 volts to the sensor. As coolant temperature changes, the internal resistance of the sensor will change, causing a varying voltage drop across the sensor. The engine controller reads the voltage drop across the sensor as engine coolant temperature.

To make the sensor more accurate, the 5 volt signal goes through a 10,000 ohm resistor or a 909 ohm resistor circuit in side the engine controller. If the engine is cold (below 125° F.), the 5 volts is fed through the 10,000 ohm resistor. If the engine is warm (above 125° F.), the 5 volts is fed through the 909 ohm circuit.

The 10,000 ohm resistor makes the sensor very accurate at cold temperatures. Once the engine warms up the sensor becomes less accurate. The engine controller then switches the 5 volt feed through the 909 ohm resistor circuit. This make the sensor very accurate at higher temperatures. The engine controller changes scales to keep sensor readings accurate at all times.

CIRCUIT OPERATION
The engine coolant temperature sensor provides an input to the Powertrain Control Module (PCM) on circuit K2. From circuit K2, the engine coolant temperature sensor draws up to 5 Volts from the PCM. The sensor is a variable resistor. As coolant temperature changes, the resistance in the sensor changes, causing a change in current draw. The K2 circuit connects to cavity 2 of the PCM.

The PCM provides a ground for the engine coolant temperature sensor signal (circuit K2) through circuit K4. Circuit K4 connects to cavity 4 of the PCM connector.