Checking The Engine Coolant Temperature (ECT) Sensor

Purpose:
The Engine Coolant Temperature (ECT) 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 engine coolant.

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

Based on the amount of voltage drop at the coolant sensor, the PCM will, adjust the fuel injector pulse width (a cold engine will receive a longer pulse width, allowing for a richer mixture), compensate for condensation of fuel in the intake manifold, monitor and adjust engine warm-up speed, advance ignition timing when the engine is cold, and activate the Electric EGR Transducer (EET) to prevent vacuum from reaching the EGR valve.

Coolant Temperature Sensor Resistance Test:

1. With key off, disconnect connector from coolant temperature sensor.
2. Connect ohmmeter across coolant temperature sensor. Resistance should read as follows;
   • 700 to 1,000 Ohms at approximately 200°F (operating temperature).
   • 7,000 to 13,000 ohms at approximately 70°F, (room temperature).
3. If resistance is not within specifications, replace sensor.

As always, check the service manual for the proper procedures and specifications for your particular vehicle.