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Causes and Symptoms of a Bad Intake Air Temperature (IAT) Sensor

Symptoms of a Bad Intake Air Temperature (IAT) Sensor
An IAT sensor is an important component that is needed while starting up a vehicle's engine. A faulty sensor can decrease the life of the engine and reduce the efficiency of fuel consumption. Take a look at the symptoms and understand why such a problem occurs.
Anuj Mudaliar
Last Updated: Mar 19, 2018
One Device, Many Names
IAT sensors are known by various names depending on the manufacturer. Those from General Motors are called manifold air temperature (MAT) sensors, while those from Ford are called either vane air temperature (VAT), air charge temperature (ACT), or manifold charging temperature (MCT) sensors. Those manufactured by Bosch are called air temperature sensors (ATS), and Chrysler makes charge temperature sensors (CTS).
Functions of an IAT Sensor
An intake air temperature sensor is an essential component of an engine, which ensures that the vehicle starts smoothly, and that the fuel-to-air ratio is maintained at appropriate levels, for effective combustion of the fuel when the engine is cold. In some vehicles, it is used to delay the release of the exhaust gas recirculation valve, and decreases the time taken for the engine to warm up.
What Causes a Bad IAT Sensor
The IAT sensor can be damaged by backfiring of the engine. The sensor can also show faulty readings due to accumulation of oil and carbon, wear and tear over time, and a poor connection after servicing the air filtering unit. We shall now check out the various warning signs that one should look out for, and tests to identify a malfunctioning air temperature sensor.
Failure Symptoms of an IAT Sensor
-Rough idling when engine is cold
-Knocking sound from engine
-Slow ignition starts
-Stalling engine
-Engine stumbling in revolutions when cold
-Sudden surges in engine revolutions after warming up
-Check engine signal on dashboard lights up with error code for a malfunctioning sensor
The above symptoms of a bad intake air temperature (IAT) sensor are not a foolproof way of determining the problem, because they are common for a few other malfunctioning components as well, such as mass air flow sensor, oxygen sensors, coolant temperature sensor, etc. So, to make sure that the IAT sensor is the actual one to blame, a few tests need to be carried out.
Testing an IAT Sensor
Testing for a faulty IAT sensor is not very difficult, and requires only a scanning tool, a multimeter, and a wire piercing probe. This process is inexpensive, and is always a good idea before going in for a replacement. To use the scan tool, you need to perform the following steps.
  1. Attach the scan tool to the vehicle, and turn on the engine.
  2. After turning it on, check for the temperature of the IAT sensor. It should be 10°F above or below the ambient temperature of the vehicle. If this is not the case, you may have a problem with the sensor.
  3. Shake the IAT sensor connection to the mass air flow sensor, and check to see if there is any difference in reading. A change in the reading indicates a bad connector, which then has to be replaced.
  4. If the temperature reading displays -30 to -40°F, the dashboard light should show the code P0113, and if the reading displays 300°F, the dashboard should show the code P0112.
  5. If the reading shows a temperature of 300°F, you need to check if the MAF sensor wires are shorted because of the internal copper getting exposed to each other. Remove all electrical tape to examine the wires and check for signs of damage.
  6. Separate the shorted wires and check if the readings turn normal; if not the connector needs to be replaced.
  7. Disconnecting the IAT from the MAF should get the temperature reading back to -30 to -40°F. However, if this does not happen, it means that there could be a problem with the vehicle's internal computer, which needs to be checked and solved by a technician.
  8. Connecting the 2 IAT wires with jumper cables should change the temperature to 300 °F. If this does not happen, it might mean that the wiring or the computer is bad.
  9. Now, to test the IAT sensor with a multimeter, you should measure the resistance of the sensor. If the multimeter shows a reading of 0 to 47 Ohms, then you have a problem with the sensor.
Testing an IAT Circuit Malfunction
The only thing remaining is to check for a circuit malfunction in the IAT sensor. To do this, there are a few important things to keep in mind: Never touch the MAF sensor connector with the leads of the multimeter from the front. You can either use specially designed back probes or wire piercing probes. Now, to check the circuits, perform the following procedure:
  1. Disconnect the MAF connector.
  2. Switch the multimeter to Volt Direct Current mode. Now, connect the red multimeter lead to wire B and the black lead to wire A.
  3. With your engine running, the multimeter should show a reading of 4.5 - 5 volts. If this does not happen, it means that the internal computer is to blame, and that it is not producing the voltage that the IAT sensor needs to function.
To fix a faulty intake air temperature sensor, remove all carbon and oil accumulation. If this does not fix the problem, replacing the unit is the best option.