Coolant Temperature Sensor/Switch (For Computer): Description and Operation

Wiring Diagram:

DESCRIPTION
The ECT sensor is a thermistor (a resistor whose resistance changes as a function of temperature) and is mounted in the engine coolant stream. The ECT sensor is a "two-wire" sensor with a reference voltage and a ground provided by the ECM/PCM. Low coolant temperature produces a high resistance and high temperatures result in a low resistance.

OPERATION
The ECM/PCM supplies a five-volt signal to the coolant sensor through a resistor in the ECM/PCM and measures the signal voltage. The voltage will be high when the engine is cold and low when the engine is hot.

The ECT sensor provides engine coolant temperature information to the ECM/PCM for fuel enrichment, ignition timing, air management, idle speed control and closed loop fuel control.

A failure in the ECT sensor circuit should set a DTC P0115 or P0116.

Legend

1. Crankshaft Position Sensor
2. Engine Coolant Temperature (ECT) Sensor
3. Intake Air Temperature (IAT) Sensor
4. Manifold Absolute Pressure (MAP) Sensor
5. Engine Control Module (ECM) / Powertrain Control Module (PCM)
6. Circuit Opening Relay
7. EFI-HTR Relay
8. Heated Oxygen Sensor 2(HO2S 2)
9. Oxygen Sensor (O2S)