How To Test The Intake Air Temp (IAT) Sensor (GM 3.5L)

TEST 3: IAT Sensor Circuit Low Voltage

You've been directed here from TEST 1 because your scan tool has confirmed that the IAT sensor is reading an air temperature of 300 °F.

You have also retrieved a P0112 Diagnostic Trouble Code (IAT Sensor Circuit Low Voltage) from the PCM's memory.

In this test step, we're gonna' further troubleshoot this problem. The two most likely causes (of this code and the temperature reading) will be:

• The IAT sensor wires have shorted together.
• Or a bad intake air temperature (IAT) sensor.

OK, this is what you need to do:

1. Connect your scan tool and get to its Live Data mode.
2. Scroll down to the PID for the IAT Sensor.
   • 300 °F temperature reading should still be present.
3. Now, remove the black plastic loom from the MAF sensor wires (about 6 inches from the connector).
4. Remove any black electrical tape that may be wrapped around the wires.
   • What you're looking for, as you remove this black electrical tape is to see if the wires are shorted together.
5. If the IAT sensor wires are shorted together you'll notice that:
   • The insulation has peeled of exposing the copper inside the wires.
   • At certain points, the copper wires are (or were) touching each other.
   • NOTE: the IAT sensor wires are the one labeled with the letters D and E in the image viewer.

Let's interpret your test results:

CASE 1: The IAT sensor wires were shorted together- This tells you that you that the connector is bad and needs to be replaced.

You can verify that this is the repair solution by separating the wires that are shorted together and then checking the intake air temperature PID (on your scan tool) to see if the temperature has gone from 300 °F to a temperature that is ±10 °F of ambient temperature.

CASE 2: The IAT sensor wires WERE NOT shorted together- This tells you that the MAF sensor connector is OK.

The next step is to unplug the IAT sensor from its connector and see if the temperature reading on your scan tool changess to -30 to -40 °F. For this test, go to: TEST 4: Unplugging The IAT Sensor.

TEST 4: Unplugging The IAT Sensor

If you've reached this test, you have confirmed that your the IAT sensor wires are not shorted together (TEST 3) and that your scan tool is still showing a 300 °F intake air temperature sensor reading.

There are two things that need to be done, before we condemn the IAT Sensor as bad.

The first one (and the focus of this test) is to make the PCM think the IAT sensor is reading -30 °F. By making the PCM see -30 °F, we'll eliminate the PCM as bad.

The second thing is to directly check the resistance of the IAT sensor itself (with the connector disconnected) and we'll do this in TEST 6.

OK, here's what you'll need to do:

1. Connect your scan tool to your vehicle and:
   • Turn the key to the ON position.
   • Go to Live Data mode.
2. Scroll down to the IAT Sensor PID.
   • The IAT sensor should be reading 300 °F.
3. Disconnect the mass air flow (MAF) sensor from its connector.
4. Once you disconnect the MAF connector the IAT Sensor PID should read:
   • -30 to -40 °F.
   • If you check for Codes, you should see a P0113: Intake Air Temperature (IAT) Sensor Circuit High Voltage.
5. When done, turn the key Off and interpret your results below:

CASE 1: Your scan tool showed -30 to -40 °F- This is the normal result from unplugging the IAT Sensor (MAF connector) and tells you that the PCM is OK.

The next step is to check the resistance of the IAT sensor itself (unplugged from its connector). For this test, go to: TEST 6: IAT Sensor Resistance Test (P0112).

CASE 2: Your scan tool DID NOT show -30 to -40 °F- This tells you that the there's something wrong with the wiring harness or the PCM itself.

Now, checking the wiring between the PCM or the PCM itself is beyond the scope of this tutorial but you have at least eliminated the intake air temperature (IAT) sensor inside the MAF sensor as bad.

Before checking anything else, I suggest that you do TEST 8: 5 Volt Reference Circuit.