TEST 5: Jumpering The IAT Sensor Circuits

How To Test The Intake Air Temperature (IAT) Sensor (Toyota Corolla 1.8L)

If you've reached this point, you have verified several important things about the IAT sensor on your Toyota and they are:

One: That a P0113 is stored in your Toyota's computer's memory.

Two: TEST 1 showed that the IAT sensor PID (on your scan tool) is showing an extremely cold temperature of -40 °F (-40 °C) or colder.

Three: The wiggle test confirmed that there are no problems with the MAF sensor's connector (TEST 2).

The next step, is to use a jumper wire and jumper the two IAT sensor wires together. These two are the ones labeled with the numbers 4 and 5 of the MAF sensor connector in the photo above.

If all is OK in the wiring and in the PCM... after jumpering these two wires together, the PCM will read a temperature of 284 °F (140°C) or higher, and will set a DTC P0112: Intake Air Temperature (IAT) Sensor Circuit Low Voltage.

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

  1. Keep your scan tool connected to your vehicle.
  2. Disconnect the mass air flow (MAF) sensor from its connector.
  3. Locate the wires identified with the number 4 and number 5.
  4. Jumper these 2 wires together with a jumper wire.
  5. Turn the key to the ON position (RUN position)
  6. Let the scan tool power up and go to Live Data mode.
    1. Scroll down to the IAT sensor PID (see photo 3 of 3).
  7. Your scan tool should now read 284 °F (140°C) or higher for the intake air temperature (IAT) sensor reading.
    1. You'll also see DTC P0112.

Let's analyze your test results:

CASE 1: The scan tool registered 284 °F (140°C) or higher - This test result tells you that the wiring between the PCM and MAF sensor connector is OK and that the PCM is not fried.

The next step is to check the internal resistance of the intake air temperature sensor to see if it has an ‘open’.

For this test, go to: TEST 7.

CASE 2: The scan tool DID NOT register 284 °F (140°C). Make sure that you're testing the correct wires, that your connections are OK, and repeat the test.

If you get the same reading on your scan tool after repeating the test, then this tells you that you have a problem in the wiring between the IAT sensor and the PCM or that the PCM is fried (although a bad PCM is rare).

The next step for you, is to make sure that the IAT sensor is getting power and Ground from its two wires. For this test, go to: TEST 8.

TEST 6: IAT Sensor Resistance Test (P0112)

How To Test The Intake Air Temperature (IAT) Sensor (Toyota Corolla 1.8L)

If you've reached this point, you have already performed: TEST 1 and have verified that the IAT sensor's PID is reporting an extreme hot temperature (284 °F (140°C) or higher).

You've done TEST 3 and confirmed that the IAT sensor's 2 wires aren't shorted together.

You've done TEST 4 and saw that the IAT sensor's PID showed an extreme cold temperature (-40 °F (-40 °C) or colder) when you unplugged the MAF sensor's electrical connector.

The next step is to to check the resistance of the intake air temperature (IAT) sensor with your multimeter in Ohms mode.

This will check to see if the IAT sensor has shorted together inside the MAF sensor and causing a resistance between 0 and 47 Ohms.

If the intake air temperature (IAT) sensor is producing a resistance between 0 and 47 Ω's., then the PCM will output a temperature of 284 °F (140°C) or higher, and set diagnostic trouble code (DTC) P0112: Intake Air Temperature (IAT) Sensor Circuit Low Voltage.

OK, to get this test going, this is what you need to do:

  1. Disconnect the MAF sensor connector and remove the MAF sensor.
    1. You don't have to remove the MAF sensor for this test, but I personally thinks it makes it a little easier to do this test with the MAF sensor removed.
  2. On the MAF sensor, locate the pins that correspond to the letters 4 and 5 of the MAF connector.
  3. With your multimeter in Ohms (Ω) mode:
    1. Measure the resistance of the intake air temperature (IAT) sensor.

Let's interpret your test results:

CASE 1: The multimeter recorded 0 to 47 Ohms- This tells you that the intake air temperature (IAT) sensor inside the mass air flow (MAF) sensor is bad.

Since the IAT sensor is part of the MAF sensor, you'll need to replace the entire MAF sensor to solve the P0112 diagnostic trouble code.

CASE 2: The multimeter DID NOT record 0 to 47 Ohms- So far so good, but you're not out of the woods yet.

The next step is to check the resistance you're getting to the temperature versus resistance chart in the next page.

The resistance should correspond to the outside temperature (ambient temperature) of your area. For this info, go to: IAT Sensor Temperature/Resistance Chart.

Toyota Vehicles:

  • Celica 1.8L
    • 2000, 2001, 2002, 2003, 2004, 2005
  • Corolla 1.8L
    • 2003, 2004, 2005, 2006, 2007, 2008
  • Matrix 1.8L
    • 2003, 2004, 2005, 2006, 2007, 2008

Toyota Vehicles:

  • MR2 Spyder 1.8L
    • 2000, 2001, 2002, 2003, 2004, 2005