Engine Coolant Temperature Sensor (ECT)

Engine Coolant Temperature Sensor or abbreviated ECT Sensor on vehicle has a function for measure the temperature of the water cooling of an engine. The Engine Coolant Temperature Sensor (ECT) is also often referred to as Water Temperature Sensor (WTS).

The Engine Coolant Temperature Sensor contains a thermistor and provides the Electronic Control Unit (ECU) with water cooling temperature reading. The ECU supplies a 5 voltage reference to the ECT Sensor through a dropping resistor.

When coolent temperature rises and the ECT sensor becomes hot, ECT sensor serves lower resistance. When coolent temperature decrease, then the ECT sensor server rises resistance. This feature is called thermistor type Negative Tempereture Coefisien (NTC).

The ECU uses signal from ECT infomation to make the needed calculations for :
  • Rich fuel delivery in cold condition
  • Knock sensor system
  • Avanced ignition in cold condition
  • Canister purge solenoid
  • Idle RPM control in cold condition
  • Cooling fan operation etc.

The ECT sensor has two terminals, the terminals are THA and E2. For more details note the picture below :
The Coolant temperature Meter
The ECU receives the engine coolant temperature signal from the ECT sensor. As the temperature increases, the control duty increases
Coolant Temperature
Signal (Idle)
16 %
4,2 Voltage
48 %
2,6 Voltage
48 %
2,6 Voltage
79,5 %
1,0 Voltage
The location of ECT sensor on engine is below the DCP (SOHC) or below the intake manifold (DOHC). For more details note the picture below :

  • Disconnect the ECT sensor connector, turn the ignition switch On and measure the reference voltage (reference voltage value is 4,8 – 5,2 Voltage)
  • Connect the ECT sensor connectoe and measure the voltage at the signal terminal according to engine temperature (at the temperature 80 – 900 C is 1,8 – 2,5 Voltage).
  • Disconnect the ECT sensor connector and measure the resistance of the ECT sensor.
Coolant Temperature
Coolant Temperature
1200 C
99,8 Ω
500 C
977 Ω
1100 C
131 Ω
400 C
1.460 Ω
1000 C
177 Ω
300 C
2.238 Ω
950 C
205 Ω
200 C
3.510 Ω
900 C
240 Ω
100 C
5.672 Ω
800 C
332 Ω
00 C
9.425 Ω
700 C
446 Ω
-100 C
16.160 Ω
600 C
670 Ω
-200 C
28.660 Ω
Source : Entry Level Training General Motor : Engine Management System

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