The (ECT) Engine Coolant Temperature Sensor is a temperature-variable resistor, which usually has a negative temperature coefficient.

So, The (ECT) Engine Coolant Temperature sensor is a two-wire thermistor immersed in coolant to measure its temperature.

Engine Coolant Temperature
Engine Coolant Temperature

The onboard computer uses the signal of (ECT) sensor as the main correction factor when calculating the ignition advance and the injection duration.

When the (ECT)  is high (hotter), the resistance is low.

When the (ECT) is low (cooler) the resistance is high.

Consequently, this resistance reading is sent to the vehicle’s PCM/ECM and can be used to activate emission controls. As a result, Many of the fuel, ignition, emissions and drivetrain functions handled by the PCM are affected by the engine’s operating temperature.

In addition,  the (ECT) sensor is not the same thing as a coolant temperature SENDER.

The PCM may make adjustments to any of  the following controls based on Input from the (ECT) sensor.

  • Start up fuel enrichment on fuel injected engines.
  • Spark advance and retard.
  • Exhaust gas recirculation (EGR) during warm-up.
  • Evaporative emissions control canister purge.
  • Open/closed loop feedback control of the air/fuel mixture.
  • Idle speed during warm-up.
  • Transmission torque converter clutch lockup during warm-up.
  • Operation of the electric cooling fan.

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(ECT) Sensor Possible Engine Codes:

Possible symptoms of any of these codes:

  • MIL (Malfunction Indicator Lamp) illumination will always occur
  • Vehicle may be hard to start
  • May blow a lot of black smoke and run extremely rich
  • Engine may want to die or backfire in tailpipe
  • So, your engine may run lean
  • Cooling fans may run all the time when they shouldn’t be, or not at all when they should be