1, 2, & 3 Wire Coolant Temperature Sensor Wiring Diagram: Master In 3 Min

Coolant Temperature Sensor Wiring Diagram

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The engine coolant temperature (ECT) sensor is a resistor-based sensor, which measures the temperature of the engine’s coolant. It sends the reading to the car computer (ECU), which adjusts the amount of fuel injection into the combustion chamber.

The ECT sensor comes in different wiring diagrams and colors depending upon the car. In this powerful article, we will discuss the 1, 2, and 3 wire coolant temperature sensor wiring diagram in less than three minutes.

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Coolant Temperature Sensor Wiring Diagram

Coolant Temperature Sensor Wiring Diagram
Coolant Temperature Sensor Wiring Diagram

In this powerful article, we will be more general than specific. Here you will learn a general ECT sensor wiring diagram. For your specific car’s ECT sensor wiring diagram, you should check your car’s owner manual for accurate wire color.

The wiring diagram of the coolant temperature sensor is based on year, make, and model. The color of the engine coolant temperature sensor varies and is color-coded according to the make and model. Below are the 1, 2, and 3 wire engine coolant temperature sensor wiring diagrams.

I . Single Wire Coolant Temperature Sensor Wiring Diagram

Single Wire Coolant Temperature Sensor Wiring Diagram
Single Wire Coolant Temperature Sensor Wiring Diagram

A single wire coolant temperature sensor has only one wire, which goes to the radiator fan relay.

Single Wire Coolant Temperature Sensor Wiring Diagram
Single Wire Coolant Temperature Sensor Wiring Diagram

When the temperature of the engine coolant gets hot (almost 98 degree Celsius), the single wire coolant temperature sensor’s resistance decrease (almost zero) and creates a connection of earth from the engine body.

This earth connection goes radiator’s relay 85 terminals in the fuse box to activate the relay, and the current starts to flow from the fuse box to the radiator fan, which ultimately turns ON the radiator fan.

II. 2 Wire Temp Sensor Coolant Temperature Sensor Wiring Diagram

2 Wire Temp Sensor Coolant Temperature Sensor Wiring Diagram
2 Wire Temp Sensor Coolant Temperature Sensor Wiring Diagram

The Vast majority of ECT sensors are of 2 wire type. In a two-wire coolant temperature sensor, the sensor has two wires.

  1. 5-volt Reference Wire
  2. Ground Wire

The sensor gets both of its wires from the ECU.

2 Wire Temp Sensor Coolant Temperature Sensor Wiring Diagram
2 Wire Temp Sensor Coolant Temperature Sensor Wiring Diagram

In a two-wire coolant temperature sensor, the ECU controls the radiator fan through the relay. The sensor does not have a direct connection with the radiator fan. The ECU takes the information from the coolant temperature sensor and decides to turn the fan ON or OFF.

The ECU continuously monitors the temperature of the coolant, when it reaches almost 98 degrees Celsius; the ECU then orders the radiator fan by providing an earth signal to the radiator relay in the fuse box.

When the coolant’s temperature cools down, then the ECU shuts off the radiator fan by cutting the earth signal to the radiator relay in the fuse box.

III. 3 Wire Coolant Temperature Sensor Wiring Diagram

3 Wire Coolant Temperature Sensor Wiring Diagram
3 Wire Coolant Temperature Sensor Wiring Diagram

The three-wire coolant temperature sensor is superseded by a two-wire coolant temperature sensor. A three-wire coolant temperature sensor has the following three wires.

  1. 5 Volt Reference Wire
  2. Ground Wire
  3. Earth Signal Wire for Cluster Mounted Temperature Gauge
3 Wire Coolant Temperature Sensor Wiring Diagram
3 Wire Coolant Temperature Sensor Wiring Diagram

The two wires, a “5-volt reference”, and a “ground wire” go to the ECU, and the third wire “Earth Signal Wire for Temperature Gauge” goes to the cluster-mounted temperature gauge by providing an earth signal to the temperature gauge.

In three wire coolant temperature sensors, the ECU does not control the temperature gauge in the cluster. The coolant temperature sensor provides an earth signal according to the temperature of the coolant. Higher the temperature of the engine’s coolant, the lower the resistance of the ECT sensor, and vice versa.

When the temperature of the coolant increases, the resistance of the sensor decreases, which sends high earth signal to the temperature gauge, and you see the temperature gauge indicator fully turned to the hot indication.

Similarly, when the engine coolant temperature decreases, the sensor resistance also decreases, which sends low earth signal to the temperature gauge, and the indicator rests on the cool indication.


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