Coolant temperature sensor: function and signs of failure Complete Guide

Are you worried about the health of your engine? Do you want to know how to diagnose a faulty coolant temperature sensor? Look no further – this complete guide will tell you all the essential information on coolant temperature sensors, their functions and the signs of failure. You’ll be an engine expert by the end!


This guide is designed to provide a comprehensive understanding of the coolant temperature sensor and how it works. It covers the major signs and symptoms of a faulty coolant temperature sensor, repairs, why it is an important part of your car’s cooling system, and more. The intent of this guide is to help you make informed decisions when it comes to dealing with your vehicle’s cooling system.

The following information will be explained:

  1. What is a Coolant Temperature Sensor?
  2. Signs & Symptoms of Coolant Temperature Sensor Failure
  3. Replacing your Coolant Temperature Sensor
  4. Importance of a Coolant Temperature Sensor in Your Vehicle
  5. Conclusion

Explanation of the coolant temperature sensor

The coolant temperature sensor, also known as the engine coolant temperature (ECT) sensor, is an important component that sends information to the powertrain control module (PCM), or engine control unit (ECU), about the temperature of the liquid cooling system. It is sometimes referred to as just a thermostat since it measures and monitors the engine’s operating temperature.

The PCM uses this information to regulate various systems on your vehicle, particularly for fuel injection, ignition timing, and emission systems. By monitoring and controlling these systems on our cars and trucks, vehicle manufacturers are able to make sure a vehicle runs as efficiently as possible; maximizing fuel economy and minimizing emissions.

In summary, the coolant temperature sensor helps maintain your car’s efficient running condition by providing information about its operating temperature that can be used by other systems throughout your car. Without this vital information, other components in your car could become damaged from prolonged exposure to too much heat or improper cooling or adjusting from cold weather operation.

Overview of the guide

This guide reviews the roles of the coolant temperature sensor, what it does, and how it works. It also provides an in-depth look at common signs and symptoms of sensor failure, so you can identify an issue early and get your car serviced as soon as possible. The guide is divided into four sections:

  1. Introduction to Coolant Temperature Sensors – explains why this sensor is important along with factors that affect its function and lifespan.
  2. Overview of the Guide – outlines the sections discussed in this guide in detail so you can quickly find information about a particular topic related to this sensor and how it works.
  3. Common Signs & Symptoms of Coolant Sensor Failure – discusses common signs that could indicate sensor failure or which could be indicative of another problem impacting its function.
  4. Conclusion – provides a brief summary and conclusion summarizing the topics covered in this guide in order to consolidate all pertinent information provided throughout each section for easier review and comprehension.

What is a Coolant Temperature Sensor?

A coolant temperature sensor (CTS or CTS-L) is an integral part of your car’s cooling system. It measures the temperature of the engine coolant and sends a signal to the engine’s computer to adjust accordingly. The result is more efficient cooling and better performance for your car. To get the best out of your car, it’s important to understand what a coolant temperature sensor does, how it fails, and when it needs replacing.

The main function of a Coolant Temperature Sensor is to measure the temperature of the engine coolant and send a signal to the engine’s computer indicating any changes in temperature that may need adjusting for efficient cooling. The CTS contains a thermistor which heats up when exposed to hot liquid, such as engine coolant, which causes its resistance to change. This resistance change is measured by the ECU, which sends a signal back to adjust settings in order to achieve an optimal level of performance from the vehicle by keeping temperatures consistent according to manufacturer standards.

A faulty CTS has several tell-tale signs such as bad fuel economy, stalling issues under heavy loads and excessive heat buildup in colder temperatures and during idle periods.

Function of the Coolant Temperature Sensor

The role of a coolant temperature sensor is to measure the temperature of the engine’s coolant and send this information to the vehicle’s ECU (Engine Control Unit). based on this information, the ECU can adjust the engine’s performance settings in order to ensure optimal fuel and air ratios and maximum performance. It also helps reduce emissions by signaling when adjustments need to be made. Typically, a coolant temperature sensor measures temperatures ranging from -40°C (-40°F) up to 125°C (257°F). The sensor typically uses thermistor technology, which has been around for decades and uses electrical resistance to measure temperatures. The more heat that is present, the higher the resistance will be and vice versa.

The signals from the coolant temperature sensor are fed directly into the ECU, which in turn regulates other engines components such as ignition timing, fuel injection timing and on some vehicles even adjusts turbos or superchargers in performance applications. All these components are crucial for optimal engine performance, so without a correctly working coolant temperature sensor it is not possible for an engine to work at peak performance safely. If a faulty or low-quality aftermarket parts are installed it can result in poor idle quality or misfires due to incorrect settings.

Symptoms Of Bad Coolant Temperature Sensors | AAMCO Colorado

Types of Coolant Temperature Sensors

Coolant temperature sensors come in many different varieties and can be used on a range of vehicles. There are three main types of coolant temperature sensors; discontinuous, continuous, and digital. Each type has its own unique features and benefits and should be chosen based on the specific needs of the vehicle.

Discontinuous Coolant Temperature Sensors: Discontinuous coolant temperature sensors consist of two wires that react to changes in engine coolant temperature. This type of coolant temperature sensor is typically used in older cars because it is less accurate than other types. The two wires together act as a switch that will open or close depending on changes in engine coolant temperature, which triggers the cooling fan when necessary.

Continuous Coolant Temperature Sensors: Continuous coolant temperature sensors are slightly more advanced than discontinuous sensors as they measure electrical resistance to determine the exact temperatures inside an engine’s cooling system. These sensors provide more accurate readings than their discontinuous counterparts and are typically found in newer vehicles. They measure absolute temperatures rather than just hot or cold, which helps maintain ideal temperatures inside the engine for optimal performance.

Digital Coolant Temperature Sensors: Digital coolant temperature sensors measure the fluid pressure inside an engine’s cooling system to precisely determine the exact temperatures within the system. Because they provide more detailed readings with fewer gaps in data collection, they are often used by modern cars that require more precision when gauging engine performance. They use highly sophisticated technology to track changes in temperatures over time to ensure maximum efficiency from an engine’s systems at all times.

Signs of a Failing Coolant Temperature Sensor

One common sign of a failing coolant temperature sensor is an illuminated “check engine” or “service engine soon” light on the instrument panel. This light can be the result of multiple possible issues; however, a malfunctioning coolant temperature sensor is one possible cause.

You may also notice unusual behavior from the vehicle’s cooling system, such as overheating even when the engine does not appear to be working particularly hard. The vehicle may also fail to enter closed-loop operating mode, which means that the fuel trims are not able to self-adjust and compensate for any changes in engine load and temperature.

If these signs appear, it is important to diagnose and repair them in a timely manner to avoid more serious damage to the engine and other parts of the cooling system.


If your coolant temperature sensor fails, it can cause your engine to overheat. This can be very dangerous and result in significant engine damage if not caught early. The most common symptom of a failed coolant temperature sensor is an increased engine temperature, causing the warning light or dashboard message to appear.

Other signs include steam coming out of the exhaust, white smoke emitting from the tailpipe, and an odd sweet smell in the cabin as coolant leaks into the interior. When your engine is too hot, you may also experience sudden loss of power or a lack of acceleration as fractures in internal components wear away from excessive heat.

Decreased Fuel Economy

A decrease in fuel economy can be the result of a failing coolant temperature sensor. The engine requires the correct amount of air and fuel mixture for efficient running, and the information is supplied to the ECU by the coolant temperature sensor. If it fails, incorrect readings cause the car to run too rich, which results in a decrease in mpg.

An illuminated ‘check engine’ light is also a sign that something related to this sensor may not be working properly. This can normally be identified by an OBD scan tool and with some research, you can find out what needs to be replaced.

Hard Starting or Stalling

If your engine has difficulty starting or stalls soon after starting, it can be a sign of a failing coolant temperature sensor. When the sensor does not correctly calculate the temperature of the coolant, it will not regulate fuel-to-air mixtures correctly, leading to hard starting and stalling.

In order for your car to run correctly and efficiently, it is vital for this sensor to be working properly. If you notice that your car is having difficulty starting up or stalling soon after startup, you should have the coolant temperature sensor checked for signs of failure.


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In conclusion, the coolant temperature sensor serves an important role in managing engine heat in today’s automobiles. It is responsible for providing accurate information that the computer uses to regulate cooling system operations, and it helps to prevent engine damage due to overheating.

It’s therefore important that you are aware of the signs of failure, so that you can prevent engine damage and repair any faults with the sensor if they arise. Regularly check your coolant level, listen for unusual noises from your cooling system, and pay attention to warning lights on your dashboard related to the coolant temperature.

By doing all of this and inspecting your source periodically you can ensure that your engine stays running at its optimal temperature and does not suffer any unnecessary long-term damage due to a faulty coolant temperature sensor.

Recap of the importance of the coolant temperature sensor

The coolant temperature sensor plays an important role in ensuring that your engine does not overheat and is able to operate effectively. It helps measure the temperature of the coolant travelling through your engine so that any potential coolant temperature changes can be monitored, preventing your engine from becoming too hot. The coolant temperature sensor also helps ensure adequate fuel mixture as well as spark advance under normal operation conditions.

It is therefore important that the coolant temperature sensor always functions properly, otherwise it can lead to an unreliable fuel pressure or air-fuel mix and ultimately result in poor performance of the vehicle. Symptoms such as rough idling or stalling are common signs of a faulty coolant temperature sensor, but some may be more subtle, such as an illuminated check engine light or a decrease in fuel economy. To ensure proper functioning of the engine, make sure to routinely inspect and maintain the coolant temperate sensor for optimal performance.

Importance of regular maintenance

Maintaining the coolant temperature sensor is important to ensure proper functioning of the vehicle engine. Without its regular maintenance, it’s easy for a faulty or clogged sensor to result in incorrect readings and lead to an engine that’s unable to achieve full performance. It is essential to check the coolant temperature sensor from time-to-time, especially after a long stretch of demanding driving.

Driving in heavy traffic, over rough terrain, in extreme temperatures and for extended periods can all take their toll on the sensor and push it out of its comfort zone.

In some cases, a faulty or failing coolant temperature sensor may result in visible signs of trouble such as erratic idle speed, higher-than-normal fuel consumption, decreased power output, emissions that exceed emission standards or the illumination warning lights on your dashboard. If you’re having any of these issues with your vehicle engine make sure you get it checked out by an experienced mechanic and have them look at the coolant temperature sensor as well as other parts that could be contributing to the problem.

Benefits of following safety measures

In order to ensure that the coolant temperature sensor is functioning properly, it is important to follow safety measures ahead of time. Taking preventive measures helps to maintain optimal performance, minimize the chances of failure, and maximize the life of the coolant temperature sensor. Some benefits of following safety measures include:

– Improved Engine Performance: Keeping the correct coolant temperature helps maintain optimal engine performance and fuel efficiency. This ensures smoother running after regularly scheduled maintenance and longer engine life-span.

– Lesser emissions: When the engine does not overheat, fewer emissions are released from the vehicle’s exhaust system as cooling correctly prevents potential damage and strains to other components in an internal combustion engine.

– Better Efficiency: Cooling system maintenance prolongs the life span of your cooling components, whilst providing improved efficiency helping your vehicle run faster and smoother while consuming less energy in the process.

– Reduced Repair Costs: Following preventive measure keeps your coolant temperature sensor operational at all times limiting any need for repair or replacement expenses in future which turn out as expensive investments at last.

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