Stay Cool and Confident: How to Test a Coolant Temperature Sensor with a Multimeter Like a Pro in 2024

The coolant temperature sensor maintains an engine’s optimal performance and efficiency. This small but essential component monitors the temperature of the engine coolant, providing valuable information to the engine control unit (ECU) to regulate fuel injection, ignition timing, and other critical parameters. How to test a coolant temperature sensor with a multimeter?  

Start by locating the coolant temperature sensor near the engine or radiator. Set your multimeter to the resistance or ohms setting. Disconnect the sensor’s electrical connector and connect the multimeter’s probes to the sensor’s terminals. Submerge the sensor in hot water and monitor the multimeter’s reading. The resistance should decrease as the temperature rises. If the multimeter readings deviate significantly from the specifications provided by the manufacturer, it indicates a faulty sensor that may need replacement.

In this article, I just do not explain how to test a coolant temperature sensor with a multimeter as well as I will discuss the interpreting and troubleshooting. But first, you should understand the function of the coolant temperature sensor

What is the function of the Coolant Temperature Sensor?

The coolant temperature sensor, or the CTS or ECT (Engine Coolant Temperature) sensor, is a vital component of the engine’s cooling system. Its primary function is to measure the temperature of the engine coolant and provide this information to the engine control unit (ECU).

Based on the coolant temperature readings, the ECU adjusts various engine parameters. For instance, it determines the appropriate fuel-to-air ratio for combustion, regulates ignition timing, and controls the engine cooling fan. 

Tools and Equipment Needed

Now that you understand the coolant temperature sensor and its importance, let’s gather the necessary tools and equipment to perform the testing process accurately and safely.


A digital multimeter is the most crucial tool for testing a coolant temperature sensor. A multimeter allows you to measure resistance and voltage, essential parameters for assessing the sensor’s functionality.

If you don’t have a multimeter already, you can easily find one at your local automotive store or online. Look for a multimeter with resistance and voltage measurement capabilities.

Safety Precautions

Before proceeding with the testing process, it’s essential to prioritize safety. Here are a few safety precautions to keep in mind:

Park the Vehicle in a Safe Area 

How to Test a Coolant Temperature Sensor with a Multimeter

Ensure you park in a well-ventilated space, preferably outdoors or in a garage with good airflow. Avoid testing the sensor in confined or enclosed spaces.

Allow the Engine to Cool Down 

Testing a coolant temperature sensor requires working with the engine and its components. To prevent accidental burns, ensure the engine has cooled down sufficiently before beginning the testing process. Waiting at least an hour after turning off the engine is recommended.

How to test a coolant temperature sensor with a multimeter? Step by step guideline

Now that we have all the necessary tools and precautions let’s dive into the step-by-step process of testing a coolant temperature sensor using a multimeter. Following these instructions can determine whether the sensor is functioning correctly.

step#1 Locate the Coolant Temperature Sensor

To test the coolant temperature sensor, you need to locate it first. The coolant temperature sensor is typically positioned near the engine block or radiator. It may vary in its exact location depending on the vehicle’s make and model.

To find it, consult your vehicle’s manual or online resources that provide specific guidance on locating the sensor. Look for a sensor with wires connected to it, often with a single or multiple terminals.

step#2 Set the Multimeter

how to test a coolant temperature sensor with a multimeter

Before conducting the test, you need to set your multimeter to the appropriate setting. Turn the dial or select the resistance or ohms setting on your multimeter. This setting allows the multimeter to measure the resistance of the coolant temperature sensor accurately.

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Ensure that the multimeter leads or probes are properly connected to the corresponding ports on the multimeter for resistance measurement. This ensures that the multimeter is ready to read and display the resistance values accurately.

step#3 Disconnect and Connect

You’ll need to disconnect the electrical connector attached to the coolant temperature sensor. The electrical connector might have a locking mechanism or require pressing or pulling to release it gently. Take note of the type of connector and its release mechanism.

Once the connector is disconnected, attach the multimeter’s probes to the terminals on the coolant temperature sensor. Ensure a secure and firm connection between the multimeter probes and the sensor terminals. This connection allows the multimeter to measure the resistance of the sensor effectively.

step#4 Submerge in Hot Water

To simulate engine conditions, you need to submerge the coolant temperature sensor in hot water. Prepare a container of hot water, ensuring that the temperature is high enough to replicate the typical operating temperature of the engine but still safe to handle. Carefully place the coolant temperature sensor into the hot water, ensuring it is fully submerged.

step#5 Monitor the Reading

As the coolant temperature sensor is submerged in the hot water, you’ll need to monitor the multimeter’s reading. The multimeter may take a few moments to stabilize and display an accurate reading. Observe any changes in the resistance or ohms values displayed on the multimeter screen.

These readings correspond to the temperature being simulated by the hot water. Monitoring the multimeter’s reading allows you to assess the response of the coolant temperature sensor to changes in temperature.

step#6 Compare with Specifications

After obtaining the multimeter readings, you should compare them with the specifications provided by your vehicle’s manufacturer or the sensor manufacturer. These specifications indicate the expected range of resistance values for the coolant temperature sensor at different temperatures.

By comparing the multimeter readings to the specified range, you can determine if the coolant temperature sensor is functioning correctly. Significant deviations from the specified range may indicate a faulty sensor that needs to be replaced.

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Analyzing the Test Results

After performing the tests on the coolant temperature sensor, it’s time to analyze the readings obtained from the multimeter. you can determine the sensor’s functionality by interpreting these readings and identifying potential issues.

Ideal Resistance and Voltage Values

To evaluate the test results accurately, it’s essential to understand the ideal resistance and voltage values for a properly functioning coolant temperature sensor.

These values may vary depending on the vehicle’s make and model, so it’s recommended to consult the vehicle’s repair manual or manufacturer’s specifications. However, as a general guideline:


A functional coolant temperature sensor typically exhibits a resistance value within a specific range. Deviations from this range may indicate a faulty sensor. Refer to the repair manual or manufacturer’s guidelines for the ideal resistance values relevant to your vehicle.

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When testing the sensor’s voltage, you should generally observe a fluctuating voltage reading. The voltage should increase as the engine warms up and decrease as it cools down. This behavior indicates that the sensor is accurately responding to temperature changes.

Interpreting Readings and Troubleshooting

Based on the resistance and voltage readings obtained from the multimeter, you can interpret the results and troubleshoot any potential issues. Here are a few scenarios to consider:

Normal Readings

The coolant temperature sensor functions correctly if the resistance and voltage readings fall within the expected range. In this case, you can conclude that the sensor is not the cause of any engine performance issues you may be experiencing.

Abnormal Readings

If the resistance or voltage readings deviate significantly from the expected range, it suggests a potential problem with the coolant temperature sensor. Abnormal readings can indicate a faulty sensor, wiring issues, or other underlying problems. It’s important to investigate further and troubleshoot to identify the root cause.

Possible Causes of Abnormal Readings

If you obtain abnormal readings, several factors should be considered when troubleshooting the issue. It could be a faulty sensor, damaged wiring or connectors, a malfunctioning ECU, or even an engine coolant problem. Checking for loose connections, damaged wires, or coolant leaks can help narrow down the possible causes.

Common Signs of a Faulty Sensor

how to test a coolant temperature sensor with a multimeter

When the coolant temperature sensor starts to malfunction, it can lead to several issues that affect the performance and reliability of your vehicle. Here are some common signs to look out for:

Inaccurate Temperature Readings 

The dashboard temperature gauge may display incorrect readings, showing the engine as cooler or hotter than it is. That means your sensor is not working.

Poor Fuel Economy 

A faulty sensor may cause the engine to run rich or lean, decreasing fuel efficiency and potential waste. Poor fuel economy may increase your cast.

Engine Overheating 

If the sensor fails to relay accurate temperature data to the ECU, the engine cooling system may malfunction, resulting in overheating.

Difficult Cold Starts

A faulty coolant temperature sensor may send incorrect signals to the ECU in colder weather conditions, causing difficulty starting the engine.

Check Engine Light 

A malfunctioning coolant temperature sensor can trigger the check engine light on your vehicle’s dashboard, indicating a potential problem that needs attention.

Additional Considerations

In addition to the testing process, there are a few additional considerations to keep in mind regarding the coolant temperature sensor. These considerations will help you ensure accurate readings and maintain the optimal performance of your vehicle’s cooling system.

Testing the Sensor in Different Temperature Conditions

It’s beneficial to test the coolant temperature sensor in various conditions to obtain comprehensive results. This means conducting tests when the engine is cold, warm, and hot.

Doing so allows you to assess the sensor’s response and accuracy across different temperature ranges, allowing for a more thorough evaluation of its performance.

Cleaning or Replacing the Sensor

If you’ve identified a faulty coolant temperature sensor through testing, you may need to clean or replace it. Over time, the sensor can accumulate debris, corrosion, or other contaminants that can affect its readings.

Cleaning the sensor with an appropriate cleaner or replacing it entirely, if necessary, can help restore proper functionality.

Consulting a Professional Mechanic

While testing the coolant temperature sensor can be done by most vehicle owners, it’s essential to acknowledge that complex issues may require professional expertise. If you encounter persistent problems or feel uncomfortable with the testing process, it’s recommended to consult a qualified mechanic. 

They can provide accurate diagnostics, perform more advanced tests, and assist with repairs or replacements, ensuring the proper functioning of the coolant temperature sensor and overall engine performance.

FAQs(frequently asked questions)

How many ohms should a coolant temperature sensor have?

The resistance value of a coolant temperature sensor can vary depending on the specific sensor and its temperature range. However, as a general guideline, most coolant temperature sensors should have a resistance of around 200 to 300 ohms when the engine is cold. As the engine warms up, the resistance should decrease steadily. 

It’s important to consult your vehicle’s service manual or contact the manufacturer for your coolant temperature sensor’s exact specifications and temperature-resistance relationship.

What are general tips for maintaining the coolant temperature sensor? 

After learning how to test a coolant temperature sensor with a multimeter, there are a few general maintenance tips to keep in mind to ensure the longevity and optimal performance of your coolant temperature sensor and cooling system.

Firstly, regularly inspect the sensor and its wiring for any signs of damage or corrosion. Clean the sensor gently using an electrical contact cleaner, but avoid harsh chemicals or abrasive materials.  

Lastly, maintain a clean radiator by ensuring it is free from debris or obstructions, as this allows for proper airflow and efficient cooling. 

What is the resistance of a temperature sensor? 

Common types of temperature sensors, such as thermistors or resistance temperature detectors (RTDs), exhibit specific resistance values at specific temperatures. 

For example, thermistors typically have higher resistance at lower temperatures and lower resistance at higher temperatures. RTDs, on the other hand, have a more linear resistance-temperature relationship.

By measuring the resistance of a temperature sensor, it is possible to determine the temperature it is exposed to, enabling accurate temperature monitoring and control in various applications, including automotive, HVAC, and industrial systems.

Are there 2 coolant temperature sensors?

Yes, it is common for some vehicles to have two coolant temperature sensors. These sensors serve different purposes within the engine system. The first coolant temperature sensor, often called the “engine coolant temperature sensor,” monitors the temperature of the engine coolant. It provides crucial data to the engine control unit (ECU) to adjust fuel mixture, ignition timing, and other engine parameters. 

The second coolant temperature sensor, known as the “cooling fan temperature sensor,” monitors the temperature of the coolant specifically for the cooling fan operation. It helps activate the cooling fan when the coolant reaches a certain temperature, assisting in cooling down the engine.

Two coolant temperature sensors allow for more precise temperature control and ensure the engine operates within the optimal temperature range, promoting performance and preventing overheating issues.


Learning how to Test a coolant temperature sensor with a multimeter is a straightforward process that can help diagnose potential issues with your vehicle’s cooling system. After reading this article, Now I hope you can confidently test the coolant temperature sensor using a multimeter.