Automotive technology: NTK explains how CTS sensors work

Correct monitoring of engine temperature ensures performance, savings and protection against engine failures and overheating

São Paulo, October 2025 – With the advancement of electronic engine management systems, o sensor CTS (Coolant Temperature Sensor), or coolant temperature sensor, has become an essential part of the performance and efficiency of modern vehicles.

The component performs an accurate measurement of the coolant temperature (refrigeration) do motor, a fundamental data for the electronic injection system, that adjusts cold start strategies, performs cooling control - which contributes to fuel economy - and acts to protect against engine failures and overheating.

The NKT - brand of Niterra, Japanese multinational also responsible for NGK -, lists signs that may indicate problems with the CTS sensor and provides guidance on how to deal with each situation:

1. Difficulty in cold starting due to incorrect information in the temperature reading, impairing the enrichment of the air/fuel mixture, with the engine cold. In flex fuel vehicles, the CTS also interferes with the activation of the cold starting auxiliary system with gasoline or fuel heating. The correction includes diagnosis with scanner, temperature comparison at some points of the engine, sensor inspection and replacement if necessary.
2. Inadequate operation of the cooling system due to defect, which can cause incorrect operation of the electric fan, electronic thermostatic valve or auxiliary water pumps. The fix involves verifying the installation, sensor resistance, correct coolant circulation and coolant condition.
3. Engine protection due to incorrect temperature measurement, what can trigger alerts on the dashboard, reduce engine power or turn off components such as air conditioning, even without real risk of overheating. It is necessary to confirm the functioning of the sensor and correct installation errors or defects in the component.
4. Failures after maintenance or replacement of parts may arise due to incorrect installation, use of inappropriate parts, coolant out of specification or in poor condition, obstruction in components such as radiator, problems with fluid circulation, system bleeding failure (to remove air from the system) and loss of pressure in the system. It is necessary to follow the application catalog of the parts involved in maintenance.
5. Tightness problems (internal or external leak) of the coolant can oxidize connectors, infiltrate the engine wiring harness and even the injection module, cause fluid loss (low level). It is recommended to check the coolant level periodically.. If you notice that the level is dropping, ask your trusted mechanic to examine the vehicle to check and correct possible leak points, inspect sensor connectors for oxidation and fluid infiltration.

Problem identification and maintenance procedures

Efficient diagnosis of the CTS sensor is performed by comparing the sensor resistance according to the temperature, using a sensor specification table as a reference. In this test we must immerse the sensor reading tip in a fluid, heating until reaching reference temperatures and carrying out resistance measurements. Another way of diagnosing is with the help of an automotive scanner., engine temperature monitoring from the cold phase to the normal operating phase, comparing the temperature measured on the scanner equipment with the measurement taken on the engine, with the help of an automotive thermometer.

The sensor uses NTC technology (Negative Temperature Coefficient), where resistance decreases as temperature increases, allowing accurate readings. Some vehicles may have more than one CTS sensor, depending on the complexity of the cooling system. Some mechanics perform the test only via scanner equipment, monitoring from the cold phase to the activation of the electric fan, However, this test alone does not guarantee the correct functioning of the system..

“The CTS sensor is decisive in ensuring engine efficiency and fuel economy. When it fails, may compromise drivability, damage to other components such as the engine itself and even the safety of the vehicle. That is why, We always recommend proper diagnosis of the cooling system and replacement with original parts or equivalent quality”, explains Hiromori Mori, Niterra Technical Assistance Consultant.

When changing a sensor is necessary, It is important to follow fundamental steps: accurate diagnosis, Use of the correct part consulting the updated catalog, cleaning the system before installation, application of appropriate torque and test operation. Some models still require the procedure to remove air from the system (“sangria do ar”), when the system has more than one temperature sensor, piloted thermostatic valve and electric water pump, they must be tested to ensure the correct functioning of the system.

Niterra do Brasil, through its NGK and NTK brands, offers a series of products aimed at the automotive maintenance market, ranging from spark plugs and ignition coils to a series of sensors applied to the engine and braking system.