Every vehicle engine is a fine-tuned machine with several systems and components that work harmoniously for optimum performance. These systems and components malfunction over time and affect the overall engine performance.
While every system and component has a specific function, car sensors are essential for the car computer to function properly. For instance, the intake air temperature sensor detects the temp of the airflow entering the engine and relates this data to the engine control module (ECM).
Since the intake air temperature sensor can fail and pose drivability issues, motorists should be aware of intake air temperature sensor symptoms and what to do. Here, we’ll discuss intake air temperature sensor functions, symptoms, and how to fix them.
What Does The Air Intake Temperature Sensor Do?
The intake air temperature sensor, also known as the IAT sensor, is a vital component that helps in engine efficiency. It monitors the temperature of the air entering the engine and communicates the data to the powertrain control module (PCM).
The PCM then directs the proper air-fuel mixture ratio for a proper combustion process. For example, if the IAT sensor detects warm air entering the engine since the air density is less, the car computer will send less fuel for proper mixtures and efficient engine performance.
Therefore, if the IAT sensor malfunctions, the engine will suffer significant changes in the engine performance.
How Does Air Intake Temperature Sensor Work?
Auto manufacturers usually install the IAT sensor on top of the intake manifold or between the air filter housing and the intake manifold so the tip can sense air passage. On vehicle engines that monitor the air volume with a MAF sensor, the MAP sensor also works as an Intake air temperature sensor.
Some manufacturers mount two intake air temperature sensors on V-type engines. This is so common on engines with separate or split intake manifolds. How important is the intake air temperature sensor, anyway?
An intake air temperature sensor is a thermistor. This means that its signal varies depending on changes in the temperature.
It works in the same similitude as the coolant sensor. The car computer applies a reference or resistance voltage to the sensor and then determines the air temperature from the voltage it receives back from the sensor.
The return voltage changes in direct proportion to the changes in air temp. The changes in the sensor resistance affect the voltage that returns to the car computer.
In some vehicles, automatic climate control systems also work with air temperature sensors. Some air-temperature sensors monitor the ambient air and the air inside the passenger compartment.
Kindly note that the climate control systems have their temperature sensor placed outside the engine bay, so engine heat will not affect the reading. Automakers usually mount the climate control air temp sensor in the cowl area or behind the grille.
These climate control air temperature sensors work like the IAT sensor. However, some of them use infrared sensors to read the vehicle’s occupant temperatures.
Intake Air Temperature Sensor Symptoms
A lousy intake air temperature sensor will trigger a check engine light on the dashboard and cause several engine performance issues.
Check engine light
The car computer monitors all system operations in a vehicle. If any system or sensor malfunctions, it will illuminate the check engine light on the dashboard. The engine warning light will notify the driver of any underlying issues in the system.
In the same manner, if the IAT sensor fails, the warning light will pop up on the instrument cluster. Therefore, whenever this light illuminates on the instrument cluster, diagnose the vehicle with a diagnostic scan tool to know what’s wrong with the system.
Vehicle engines should idle as smoothly as possible. A rough idling shows one or more systems or components are malfunctioning. It could be you have a faulty IAT sensor causing an improper air-fuel mixture ratio.
If the engine gives small hiccups on idle, the intake air temperature sensor is bad. Like check engine light, several issues can cause rough idling.
Bad gas mileage
The engine control unit constantly adjusts the air-fuel mixture to ensure maximum fuel economy. Here’s the catch; the engine control unit relies on several sensors like IAT, MAF, and MAP sensors to adjust the air-fuel mixture.
If any of these components go bad, it’ll significantly increase or decrease gas mileage. If you spend fewer miles per gallon, it could mean you have a lousy IAT sensor.
Engine misfire is a common BMW intake air temperature symptom. An improper air-fuel mixture in the combustion chamber can cause the engine to misfire. Again, several factors can cause the engine to misfire. It could be bad spark plugs, lousy spark plug wires, fuel injectors, faulty IAT sensors, etc.
Engine misfire will affect acceleration. Since there are several causes of engine misfires, always diagnose your engine whenever it misfires to track the culprit.
A faulty IAT sensor’s false reading will cause the powertrain control module to think the air is colder or warmer than it is. This will make the PCM miscalculate the air-fuel mixture, leading to a poor or drop in acceleration.
Hard starting in cold weather
Believe it or not, your car needs more fuel during start-up. It needs more and the correct amount of fuel. If the car computer injects an obscene amount of fuel during startup because of a lousy IAT sensor, you’ll experience hard starting, especially in cold weather conditions.
EGR valve affected
In some vehicles, the PCM controls the EGR valve operation with air temperature. This means a lousy IAT sensor can affect the EGR valve operations. A malfunctioning EGR may affect the overall engine performance.
How Do You Test An Intake Air Temperature Sensor?
If you notice any of the symptoms above, test the IAT sensor to know if it is the culprit. In the following sections, we’ll look at how to test an IAT sensor with a multimeter. Kindly, note that an IAT sensor can be an integral part of a MAF or MAP sensor. They can also be independent sensors depending on the vehicle design.
Allow your engine to cool before you start this test.
Testing the IAT sensor resistance
- Disconnect the electrical wiring connector
- Set your multimeter on an auto range or 50k on the OHMs scale
- Turn off the engine and measure the resistance on the IAT sensor. At about 20 degrees centigrade or 68 degrees Fahrenheit, the multimeter should record 37k ohms. At 30 degrees centigrade or 86 degrees Fahrenheit, you should get 24k ohms.
- Reconnect the IAT wiring harness
- Start the engine and allow it to idle for 15-20 minutes. You can also leave it idling until the radiator fan activates to allow the engine to reach normal operating temperature.
- Switch off the vehicle
- Disconnect the IAT wiring connector
- With the intake air temperature sensor unplugged, re-check the sensor resistance across the terminals. At 90 degrees centigrade or 194 degrees Fahrenheit, you should have 2.8k ohms. At 100 degrees centigrade or 212 degrees Fahrenheit, you should have 2k ohms.
Consult your service manual for your vehicle-specific temperature and the resistance value of the intake air temperature sensor.
Testing the IAT sensor power and ground
This test aims to ensure the PCM provides the required IAT reference voltage (usually 5 volts) and the ground to process the circuit reading.
- Turn off the vehicle
- Switch the DMM to DC voltage scale
- Disconnect the intake air temperature sensor wiring connector
- Back probe the IAT’s signal wire on the connector using the DMM’s red probe.
- Connect the black probe on the negative battery terminal or the engine ground
- Switch the ignition to the ‘ON’ position. You should have 4.6 to 5 volts
- Return the ignition key to the ‘OFF’ position
- Using the DMM’s black probe, back probe the IAT’s ground wire
- Place the red probe on the positive battery terminal
- Switch the ignition to the ‘ON’ position again. You should have 12 volts approx.
- Return the ignition key
- Reconnect the wiring harness
How To Fix Intake Air Temperature Sensor Problems
After testing the IAT sensor if you discover the sensor is bad, clean or replace it. However, I recommend replacing it. Replacing it is a pretty simple process.
- Switch off the engine and allow it to cool
- Remove the negative battery terminal
- Disconnect the IAT sensor wiring harness
- Gently pull the IAT sensor from the intake duct or unscrew it if it is mounted on the intake manifold
- Install the new IAT sensor and reconnect the wiring harness
- Fix the negative battery terminal and tighten it properly.
Q: Will a bad IAT sensor throw a code?
If the intake air temperature sensor fails and starts sending false readings to the engine control module, it’ll register a P0113 error code. The check engine light will accompany the fault code.
The car computer can log the P0113 fault code because of several parameters. It could be a dirty air filter, damaged wiring, lousy mass airflow sensor, or a faulty PCM.
Q: Where is the intake air temperature sensor located?
Depending on your vehicle engine design, the intake air temperature sensor can be located on the air cleaner housing, intake manifold, or the air intake boot.
You may find it difficult to locate or may not even see the IAT sensor in your vehicle. Here’s why; some auto manufacturers built the IAT sensor with the MAF or MAP sensor.
Q: Does the ambient air temperature sensor affect the engine?
The ambient air temperature does not play any role in the engine efficiency and gas mileage. However, it’ll affect the engine power output. Therefore, do not mistake engine power output for efficiency. Power output and engine efficiency are two different things.
Q: Can you clean an intake air temperature sensor?
The intake air temperature sensor is a vital component that measures intake air temperature. The IAT tip is exposed to air passages and can get dirty. If the sensor becomes dirty, you can clean it for efficient reading.
You may wonder what to use to clean the intake air temperature sensor. If the sensor is dirty, uninstall and clean it with an electronic cleaner.
Q: How much is an intake air temperature sensor?
Intake air temperature sensor price varies from vehicle to vehicle. However, on average, an IAT sensor should cost between $80 and $150. Labor charges should be around $30 to $50. The sensor itself should be around $50 to $100.
On some vehicles, the sensor can be as low as $25 and as high as $200 on high-performance cars.
The intake air temperature (IAT) sensor plays a critical role in the overall engine performance. Since a lousy IAT sensor can affect engine efficiency and optimum performance, if you notice any of the intake air temperature sensor symptoms, fix it as soon as possible.
You can test and fix it following the procedures in this piece or have a professional mechanic fix it.