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What is a cooling system temperature sensor?

What is a cooling system temperature sensor?

Every driver knows that coolant/antifreeze is needed to keep the engine running at optimum temperature. But how does the cooling system know when the engine is at the right temperature? The coolant temperature sensor plays a critical role in engine operation.

The coolant temperature sensor is a sensor that determines the coolant temperature and informs the driver if the engine is overheating. The coolant temperature sensor informs the engine control unit of the engine's operating temperature so that the amount of fuel and ignition timing can be adjusted accordingly.  If the sensor detects a temperature that is too high, it triggers the engine overheating warning light.

On this page, we'll explain how the coolant temperature sensor works and show you how to troubleshoot it.

What is a temperature sensor and how does it work?

The coolant temperature sensor is a component of the cooling circuit that measures the temperature of the coolant in the system, provides an indication of the heat generated by the engine, and warns the driver if the engine is overheating. The sensor is linked to the engine control unit and constantly monitors the coolant temperature to ensure the engine is running at the optimum temperature.

To get an accurate reading of the current engine temperature, the ECU or Powertrain Control Module (PCM) sends a regular voltage to the sensor. The sensor's resistance changes with temperature, allowing the control unit to track temperature changes. The PCM uses this data to calculate the coolant temperature and then adjusts fuel injection, fuel/air mixture and the cooling fan on/off. This information is also used to provide an accurate gauge reading on your dashboard.

Where is the coolant temperature sensor located?

The coolant temperature sensor is located in the heart of the engine, near the cylinder head. This is where the engine temperature is highest. It consists of four wires and transmits the engine temperature in real time to an ECU. The ECU then determines whether the temperature conditions are right for the vehicle to run properly. If the sensor detects an excessive coolant temperature at this point, it triggers the engine light to come on. As soon as this light comes on, it's imperative to stop the vehicle because it means the engine temperature is much too high and could lead to total engine failure.

What are the symptoms of a failed coolant temperature sensor?

The coolant temperature sensor is not a consumable part. Therefore, it is difficult to know when the sensor is no longer functioning properly. If the coolant temperature sensor is defective, the driver will no longer be alerted to engine overheating by the coolant overheat warning light on the instrument panel. However, it is possible to detect signs of engine overheating by observing the following symptoms

  • White smoke from the hood;
  • Loss of engine power;
  • Strange engine noise at idle
  • Engine light on the dashboard
  • Irregular dashboard gauge readings (temperature should be between 88 and 90° C when the engine is warm)
  • Engine overheating (as indicated by the dashboard gauge)
  • Limited performance (due to PCM miscalculation of fuel mixture)
  • High fuel consumption

Engine overheating can be caused by many factors. It can be caused by a lack of coolant, but also by other causes such as

  • Coolant leakage: due to a crack in the expansion tank or a leaking circuit;
  • Faulty water pump;
  • A cylinder head gasket in poor condition;
  • A radiator problem.
  • A problem with the coolant temperature sensor can have serious consequences. Engine overheating can lead to engine failure, which is extremely expensive to repair.

To replace a coolant temperature sensor

Replacing a car's temperature sensor is easy for anyone with a little mechanical knowledge and can be done in your garage. The following steps explain how to replace a faulty sensor.

Step 1: Locate the sensor

The cooling system temperature sensor is usually located in the front of the car, next to the radiator or thermostat. You may need the help of a flashlight, as it's a relatively small part located under other components in the engine compartment. Removing the engine cover may also help if it's near the thermostat housing.

Step 2: Remove the connector cable

The sensor is connected to the engine control unit by a connector that you'll need to loosen and remove. Be very careful when performing this operation, as the plastic connector and wiring can be fragile and you'll need to replace them completely if they break. Disconnect the connector and move the cable where it won't get in the way.

Step 3: Unscrew and remove the old sensor

Temperature sensors are installed the same way as spark plugs, so you need to unscrew them before removing them. Using a deep socket wrench and a ratchet, gently loosen the sensor counterclockwise without applying too much pressure. If the sensor is a little seized up, don't hesitate to spray it with a little oil. Once the sensor is slightly loose, unscrew it by hand and remove it from its seat. Coolant will likely start leaking from this point, so be prepared to replace the new sensor or drain the fluid if necessary.

Step 4: Install the new sensor

Use a rag to clean the area to remove any dirt and debris that could affect the performance of the new sensor. Place the new sensor in the thread and hand-tighten it clockwise, making sure it is properly installed. Then use a torque wrench to tighten the sensor according to the manufacturer's instructions.

Step 5: Reinstall the connector cable

With the new sensor in place, all you need to do is reconnect the cable. Make sure it's clean and connect it to the sensor, tightening all the fasteners to ensure a smooth connection with the terminal. To make sure everything is working properly, turn on the engine and watch the dashboard gauge as it heats up to make sure the temperature is consistent.

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