What is Coolant Temperature Sensor? | Signs of Bad Coolant Temperature Sensor

The engine coolant temperature sensor is one of the most important parts of the vehicle. It ensures the optimal performance of the vehicle. The function of the engine coolant temperature sensor is to measure the temperature of the coolant for the engine control unit. As the coolant temperature sensor goes bad, it produces different symptoms. This article mainly explains the working and signs of a bad coolant temperature sensor.

What is Coolant Temperature Sensor?

The coolant temperature sensor is a mechanical device that measures the temperature of the coolant in the engine. It is also called a CTS or ECT sensor. The reading of the CTS sensor shows the temperature of the engine on the car dashboard.

The normal temperature of the coolant is very important for the efficient working of the engine. If the coolant temperature becomes very high, your engine may overheat, which may lead to the failure of the engine parts. When it’s cold, the vehicle doesn’t run efficiently.

The reading of the coolant temperature sensor is sent to the ECU (engine control unit). As the ECU receives data, it utilizes this data to set and maintain proper ignition timing and fuel injection through computerized methods.

Bad Coolant Temperature Sensor Symptoms

1) Check Engine Light

If the check engine light is on, it is one of the first symptoms of a bad coolant temperature sensor. In case of a defective CTS, the “Check Engine” light comes on suddenly.

When the ECU of your engine detects a problem with the CTS sensor, it illuminates the check engine light, indicating that there is a problem with your vehicle.

As you observe the check engine light on your car dashboard, use the OBD2 scanner to look up the trouble code.

2) Poor Fuel Economy

Poor fuel economy is one of the most common symptoms of a bad coolant temperature sensor.

When the CTS fails, an error signal delivers to the CPU. The computer reactions can also upset the balance between fuel and time calculations.

Your sensor may fail without any warning and deliver a steady cold signal to the computer. The computer misread that the engine is cold, but it is still hot. Therefore, your car starts to consume too much fuel and reduces fuel consumption. Ultimately, this reduces the efficiency of the engine.

3) Electrical Cooling Fans not coming on

Few types of vehicles employ an engine coolant temperature sensor to regulate the electric cooling fan. Most cars have a fan, a dashboard display, and two separate engine management temperature sensors.

If your vehicle contains only one sensor, a bad engine coolant temperature sensor can’t efficiently operate the fan.

4) Black Smoke from the Exhaust Pipe

Your vehicle may emit black exhaust smoke due to a defective ECT sensor. If the car’s ECT sensor fails, the air-fuel ratio in the combustion chamber may be disturbed.

As the injector injects more fuel into the combustor, you can see the excess fuel burning and black smoke coming out of the tailpipe.

5) Engine Overheating

The ECT sensor plays a big role in preventing the engine from overheating. A cooling fan behind the grille extracts heat from the engine coolant. The fan is electronically controlled and depends on signals from the onboard computer.

If your sensor doesn’t work properly, then the fan gets the wrong signal; due to that, it will not start, and the engine could overheat.

6) Poor Idling

The air/fuel mixture will not properly mix due to the failure of the ECT sensor. This may cause the car to vibrate or the engine to vibrate at low speeds, causing other power losses and many other damages.

As you face poor idling issues, immediately inspect your vehicle. If you have a faulty ECT sensor, then replace it immediately.  

7) Difficult Starting Condition

The moment the car starts depends on the amount of fuel injected into the engine. If your air and fuel are not mixing properly, it may be difficult or impossible to start the car.

8) Poor Engine Performance

A faulty engine coolant temperature sensor may severely affect the air/fuel mixture. Improper mixing of the air and fuel reduces the engine performance. If the engine doesn’t work efficiently, your vehicle can’t run according to your requirements.

9) Engine Misfiring

The engine misfiring is also a major sign of a faulty ECT sensor. When the car’s ECT sensor fails, an error signal is sent to the engine control unit (ECU). The ECU then adjusts the air/fuel ratio based on these error signals.

The low air-fuel ratio can cause sudden power surges and car engine stalling due to poor fuel economy.

Coolant Temperature Sensor Replacement Cost

The replacement cost of the coolant temperature sensor varies according to the vehicle model and the type of sensor brand. The replacement cost of the coolant temperature sensor is from $40 to $260. In this cost, the labor cost is between $15 and $160, and the coolant temperature sensor cost is between $25 and $100.

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