As you might already be aware (and if you're not, well that's OK, too), the intake air temperature (IAT) sensor is part of the mass air flow (MAF) sensor.
The MAF sensor has a total of 5 wires. Three of them are dedicated to the MAF part and the other 2 are dedicated to the IAT Sensor part.
In this ‘how to test’ tutorial, I'm gonna' show you the easiest way to test the intake air temperature (IAT) sensor.
Here are the main subheadings of this article at a quick glance:
- Symptoms Of A Bad IAT Sensor.
- What Tools Do I Need To Test The IAT Sensor?
- What Does The IAT Sensor Do?
- TEST 1: Checking The Intake Air Temperature Value.
- TEST 2: IAT Sensor Circuit High Voltage.
- TEST 3: IAT Sensor Circuit Low Voltage.
- TEST 4: Unplugging the IAT Sensor.
- TEST 5: Jumpering the IAT Sensor Circuits.
- TEST 6: IAT Sensor Resistance Test (P0112).
- TEST 7: IAT Sensor Resistance Test (P0113).
- TEST 8: 5 Volt Reference Circuit.
- Intake Air Temp (IAT) Temperature/Resistance Chart.
Symptoms Of A Bad IAT Sensor
The very first thing you'll notice when the IAT Sensor goes bad inside the MAF sensor is the check engine light (CEL) shining nice and bright to let you know that there's a problem and that there's a Diagnostic Trouble Code (DTC) stored in the PCM memory.
Here are some of the specific symptoms you'll see/have:
- Diagnostic Trouble Codes:
- P0112: Intake Air Temperature (IAT) Sensor Circuit Low Voltage.
- When your scan tool reports this DTC, the IAT sensor is reporting a temperature of 300 °F (149 °C).
- P0113: Intake Air Temperature (IAT) Sensor Circuit High Voltage.
- When your scan tool reports this DTC, the IAT sensor is reporting a temperature of -38 °F (-39 °C).
- P0112: Intake Air Temperature (IAT) Sensor Circuit Low Voltage.
- Bad gas mileage.
- Black smoke coming out of the tailpipe.
- Won't pass the emissions test.
What Tools Do I Need To Test The IAT Sensor?
Here's a basic list of tools you'll need:
- A multimeter.
- If you need to upgrade or buy a multimeter, check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing (found at: easyautodiagnostics.com).
- Scan tool.
- Don't have one? Check out my recommendation: Abe's Scan Tool Recommendation.
- Wire piercing probe.
- Although this tool is not an absolute must, if you do buy one, you'll realize just how easy it makes testing the voltages inside the wires.
- If you need to see what this tool looks like, you can see it here: Wire Piercing Probe.
What Does The IAT Sensor Do?
In a nutshell, the intake air temperature (IAT) sensor helps the PCM (Powertrain Control Module = Fuel Injection Computer) make a correct measurement of the air mass that enters the engine by providing a temperature reading (measurement) of that air.
To get into a little more detail: the PCM needs to know two very important things (among several) to calculate the correct amount of fuel to inject for the amount of air the engine is breathing.
These two things are:
- Temperature of the incoming air.
- The flow rate of the air the engine is breathing.
The reason that the PCM needs to know the temperature of the air is because air temperature has a direct effect on air density and since the MAF sensor can only measure the flow rate of air passing thru' it, the intake air temperature sensor helps the PCM to further ascertain the precise amount of air entering the engine.
This in turn helps the PCM maximize everything from fuel consumption to performance.
OK, these are the circuit descriptions of the mass air flow (MAF) sensor and the intake air temperature (IAT) sensor:
| MAF Sensor Connector Pin Out | ||
|---|---|---|
| Pin | Wire Color | Description |
| A | Yellow | MAF Sensor Signal Output |
| B | Black w/ White stripe | Chassis Ground |
| C | Pink | 12 V. Ignition Fused Feed |
| D | Tan | Intake Air Temp (IAT) Sensor 5 Volts |
| E | Black | Intake Air Temp (IAT) Sensor Ground |
