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Understanding The Ambient Temperature Sensor

By R&D
Published on December 28th, 2023

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Vehicle manufacturers continually strive to enhance engine efficiency, reduce emissions, and improve overall vehicle performance. Among the many components that contribute to these goals, the Ambient Temperature Sensor (ATS) stands as a critical component. This article outlines operation of the ATS, reviews symptoms of malfunctions and troubleshooting of the ATS, and provices cost estimates for replacement.


The Ambient Temperature Sensor (ATS) is a key component in modern vehicles. Its primary function is to measure the ambient air temperature and provide this information to the Engine Control Module (ECM). The ECM uses this information to make real-time adjustments to various engine parameters, affecting fuel delivery, ignition timing, and emission control systems.


The ATS comes in various types. The most common of these are:

  • Negative Temperature Coefficient (NTC) Thermistors: NTC thermistors exhibit a decrease in resistance as the temperature increases. They are cost-effective, offer good accuracy, and are suitable for a wide range of automotive applications.
  • Integrated Circuit (IC) Temperature Sensors: IC Temperature Sensors are commonly found in modern vehicles. They are compact, easy to integrate into electronic systems, and can provide accurate temperature readings.
  • Infrared (IR) Temperature Sensors: Infrared sensors are used for non-contact temperature measurement by measuring the thermal radiation emitted by an object. These sensors are often used in automotive climate control systems. They can measure temperature from a distance, making them useful for cabin temperature control.

Symptoms of a Faulty ATS

A malfunctioning ATS can lead to various symptoms in a vehicle. Common signs of a faulty ATS include:

  • Reduced Engine Performance: Inaccurate temperature readings can cause the ECM to make incorrect adjustments to the air-fuel mixture, resulting in decreased engine power, acceleration, and responsiveness.
  • Increased Emissions: A malfunctioning ATS may lead to poor combustion, causing increased emissions, which can result in failed emissions tests.
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Increased Emissions

  • Poor Fuel Efficiency: Incorrect temperature data can lead to inefficient fuel management, reducing overall fuel efficiency.
  • Cold Start Problems: During cold starts, a faulty ATS may cause rough idling or prevent the engine from starting smoothly.
  • Incorrect HVAC Operation: In some vehicles, the ATS also contributes to the operation of the heating, ventilation, and air conditioning (HVAC) system. A malfunctioning ATS can lead to HVAC-related issues.

Possible Causes

  • Physical damage to the sensor or its wiring can cause it to malfunction.
  • Exposure to moisture, chemicals, or contaminants can lead to corrosion or contamination of the sensor, affecting its accuracy.
  • Electrical problems, such as a damaged or shorted wire, a blown fuse, or a faulty relay, can disrupt the sensor's operation.
  • Over time, sensors can degrade or fail due to normal wear.

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Diagnostic Tips

If a faulty ATS is suspected, use the following procedure to confirm the issue:

  • Visually inspect the sensor and its wiring for any visible damage, such as cuts, breaks, or loose connections.
  • Use a multimeter to check the continuity of the sensor's wiring and verify that the power supply to the sensor is within the specified voltage range.
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Check for Electric Connection

  • Use a diagnostic tool (such as an OBD2 Scan Tool) to check for Diagnostic Trouble Codes (DTCs) related to the sensor.
  • Refer to the vehicle’s Service Manual for instructions on how to diagnose and correct the problem.
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Innova Tool Checking for ATS

Cost of ATS Replacement

The cost of replacing an ATS can vary depending on the vehicle's make and model, the type of fan (mechanical or electric), and labor charges. The cost can range from $20 to $100 or more, including parts and labor.

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ATS Replacement


The Ambient Temperature Sensor (ATS) may be a small component, but its function in modern automobiles is critical in maintaining the balance between engine efficiency, performance, and emissions reduction. As automotive technology advances, the ATS continues to contribute to cleaner, more efficient internal combustion engines. Its presence underscores the complexity and precision of modern vehicles, demonstrating that even seemingly minor components significantly impact the evolution of the modern automotive.

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