Engine - Coolant Temperature Sensor/Switch: Description and Operation

ENGINE COOLANT TEMPERATURE (ECT) SENSOR
- Detects engine coolant temperature.
- Sensor resistance affects voltage drop across sensor terminals and provides electrical signals to PCM corresponding to temperature.
- Uses thermistor device. Resistance changes with temperature:
- Resistance decreases as temperature increases.
- Resistance increases as temperature decreases.

Operation
PCM controls the following:
1 Ignition timing
2. EGR
3. Required fuel injector pulse width
4. Shift/torque converter clutch scheduling

NOTE:
- Sensor is connected to voltage divider so that varying resistance of sensor causes a variation in total current flow. Dropped voltage across a fixed resistor in a series with sensor determines voltage signal at PCM.
- If the engine coolant temperature sensor or circuit has an open or short, Diagnostic Trouble Code No. P0ll7, P0ll8, P0125, P1116, or P1117 is output.
- If the engine coolant temperature sensor circuit fails, no torque converter lockup will occur (AT).