How To Test: P0112 OBD II Trouble Code (GM 3.8L)

Troubleshooting P0112: Intake Air Temperature Circuit Low Input

START HERE: There are 4 basic and very simple tests that'll help you troubleshoot a P0112 Intake Air Temperature Circuit Low Input diagnostic trouble code (DTC). I'll summarize what you'll be doing in this section.

Basically, you will:

1. Confirm that the IAT sensor is sensing an extremely hot air temperature (300 °F).
   • Checking the IAT sensor temperature value can easily be done with a scan tool in Live Data mode.
   • TEST 1: Checking The Intake Air Temperature Value.
2. Physically check that the IAT sensor connector's wiring is not shorted together.
   • This involves removing the hard plastic protector that's over the wires and inspecting the condition of the two IAT sensor wires.
   • You'll also need to do a simple wiggle test of the IAT sensor's 2 wires.
   • TEST 2: Checking The Condition Of The IAT Sensor's 2 Wires.
3. Making sure that the PCM can react to a big voltage drop.
   • All that you'll need to do is to unplug the IAT sensor from its connector and see if the PCM now reads an extreme cold temperature in the negative30s (-30 °F).
   • This test will help you to eliminate a bad PCM and/or a hidden electrical short somewhere in the wiring between the PCM and IAT sensor.
   • TEST 3: Disconnecting the IAT Sensor From Its Connector.

TEST 1: Checking The Intake Air Temperature Value

The first thing on our ‘to do’ list, is to see what air temperature the intake air temperature (IAT) sensor is reporting.

You can easily do this by connecting a scan tool, with Live Data capability, to your vehicle and scrolling down to the PID labeled IAT (see photo in the image viewer).

Now, it's possible to check the IAT sensor without a scan tool. How? By measuring the resistance of the IAT Sensor and them comparing them to the actual ambient temperature that your car or mini-van is in. To see the Resistance/Temperature Chart, go here: Intake Air Temp (IAT) Temperature/Resistance Chart.

If you don't have a scan tool and you need to buy one, check out my Actron CP9580 Scan Tool Review.

IMPORTANT: The engine should be completely cold before you start this test.

OK, this is what you need to do:

1. 1

   Connect your scan tool to your 3.8L GM equipped car or mini-van and turn the key to the on position (you don't need to start the engine).

2. 2

   Once the scan tool has powered up, go to its Live Data mode.

3. 3

   Scroll down to the PID labeled IAT (°F)

   1. In case you're wondering what the acronym PID stands for, it's: Parameter Identification.
4. 4

   The scan tool should register a temperature that should be within ±10 °F of ambient temperature (if all is normal)

   1. So let's say that it's 50 °F outside, then the IAT Sensor PID should register something between 40 to 60 °F.
5. 5

   Now, since you're here because you have an IAT sensor diagnostic trouble code (DTC), more than likely you'll see one of the following:

   1. - 30 to -40 °F (that's negative 30 to 40 °F).
   2. OR 300 °F.

Let's interpret your test results:

CASE 1: Your scan tool shows a 300 °F reading. This confirms that there is a problem with the intake air temperature (IAT) sensor.

This test result also confirms that the code P0112 IAT Sensor Circuit Low Voltage Input, that was stored in the PCM's memory is telling you the truth.

The most likely cause will be that the IAT sensor circuits (wires) are shorted together. This usually happens in the section of the 2 wires nearest to the IAT sensor's connector.

The next step is to physically check the condition of the wires and do a simple wiggle test. Go to: TEST 2: Checking The Condition Of The IAT Sensor's 2 Wires.

CASE 2: Your scan tool shows a -30 °F reading. This confirms that you do have a problem with the intake air temperature (IAT) sensor or its circuits.

Seeing an extreme cold temperature of -30 °F indicates one of two things, either that the IAT sensor is bad or the IAT sensor connector's wires have an ‘open’ (think unplugged sensor). You'll also see a diagnostic trouble code P0113 (IAT Sensor Circuit High Voltage) stored in the PCM's memory.

For further testing of this condition, see the following tutorial: P0113 Intake Air Temperature Circuit High Input (GM 3.8L).

CASE 3: Your scan tool shows a temperature reading that's ±10 °F of ambient temperature- This tells you that at the moment the IAT Sensor and its circuits are OK.

But, since your scan tool retrieved a DTC P0112 the problem may just be hiding at the moment, I recommend clearing the diagnostic trouble code (DTC) and road testing your vehicle to see if the code comes back.

If the P0112 DTC does come back, repeat this test once more.