Testing the intake air temperature (IAT) sensor, which is located inside the mass air flow (MAF) sensor, can easily be done with a scan tool and/or a multimeter.
In this article, I'll show you how to test IAT sensor in a step-by-step way that will help you say that, ‘Yes, it's bad’ or ‘No, it's not bad’.
Now, you may be wondering, why test it? Well, since it's part of the MAF sensor and the MAF sensor is not exactly cheap, it's a good idea to test it first before replacing it.
Contents of this tutorial:
- 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 most obvious symptom will be the check engine light (CEL) lit nice and bright on your instrument cluster. The second will be an IAT sensor malfunction 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.
- This means that the IAT sensor is reporting a temperature of 300 °F (149 °C).
- P0113: Intake Air Temperature (IAT) Sensor Circuit High Voltage.
- This means that 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.
- You'll need a multimeter to measure DC Voltage and Resistance (Ohms).
- 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.
- Although you can check the IAT sensor without a scan tool, using a scan tool with Live Data capability is the fastest and easiest way to test the IAT sensor.
- Don't have one? Check out my recommendation: Abe's Scan Tool Recommendation.
- Wire piercing probe.
- This tool makes it super easy to test 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.
The main reason why the PCM needs to know the temperature of the incoming air, is that temperature has an effect on the density of the air the engine is breathing. The denser the air, the more fuel the PCM has to inject into the engine.
Using the info provided by the MAF sensor, the PCM only gets to know the flow rate of the incoming air. With the IAT sensor, it get's to know the temperature of that incoming air and then is able to better calculate how dense that air is.
Calculating the flow rate and density of the air that the engine is breathing at any given time 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 | Black | IAT Sensor Low Reference (fancy name for Ground) |
| B | Tan | IAT Sensor 5 Volt Reference |
| C | Black w/ White stripe | MAF Sensor Ground |
| D | Pink | MAF Sensor Voltage |
| E | Yellow | MAF Sensor Signal |
