GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The intake air temperature (IAT) sensor contains a semiconductor device which changes the resistance based on the temperature. The IAT sensor is located within the mass air flow (MAF) sensor. The IAT sensor has a signal circuit and a low reference circuit. The powertrain control module (PCM) applies 5.0 volts on the signal circuit to the sensor. The PCM monitors the changes in this voltage caused by changes in the resistance of the sensor in order to determine intake air temperature.

When the intake air is cold, the sensor (thermistor) resistance is high. The PCM signal voltage is only pulled down a small amount through the low reference circuit, therefore, the PCM senses a high signal voltage. When the intake air is warm, the sensor resistance is low. The signal voltage is pulled down a greater amount, therefore, the PCM senses a low signal voltage.

When the PCM senses a signal voltage lower than the normal operating range of the sensor, this diagnostic trouble code (DTC) sets.

Conditions for Running the DTC

    â€¢ DTCs P0102, P0103, P0117, P0118, P0500, P0502, or P0503 are not set.
    â€¢ The engine coolant temperature (ECT) is less than 135°C (275°F)
    â€¢ The engine run time is more than 30 seconds.
    â€¢ The vehicle speed is 40 km/h (25 mph) or more.

Conditions for Setting the DTC

The intake air temperature (IAT) is more than 139°C (282°F) for 5  seconds.

Action Taken When the DTC Sets

    â€¢ The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    â€¢ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    â€¢ The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    â€¢ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    â€¢ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    â€¢ Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

    â€¢ If the engine has sat overnight, the engine coolant temperature (ECT) and the intake air temperature (IAT) values should display within a few degrees of each other. If the temperatures are not within 3°C (5°F), refer to Temperature Versus Resistance .
    â€¢ If you determine that the DTC occurs intermittently, performing the P1112 diagnostic table may isolate the cause of the fault.

For an intermittent, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if the malfunction is present.

  2. Using the Freeze Frame/Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can help to determine how many miles have occurred since the DTC set. The Fail Counter and the Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass or a fail. Operate the vehicle within the same Freeze Frame conditions, such as RPM, load, vehicle speed, temperature etc. that you observed. This will isolate when the DTC failed.

  3. The IAT sensor is part of the MAF sensor. An intake air temperature that is below -30°C (-22°F) indicates that the PCM and the IAT wiring are OK.

  4. Disconnecting the PCM allows using the DMM in order to check continuity of the circuits. This aids in locating an open or a shorted circuit.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

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Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Monitor the IAT display on the Engine 1 Data List of the scan tool.

Is the IAT above the specified value?

139°C (282°F)

Go to Step 4

Go to Step 3

3

  1. Turn ON the ignition, with the engine OFF.
  2. Review the Freeze Frame/Failure Records data for this DTC and observe the parameters.
  3. Turn OFF the ignition for 15 seconds.
  4. Start the engine.
  5. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
  6. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

  1. Disconnect the MAF/IAT sensor electrical connector.
  2. Observe the IAT display on the scan tool.

Is the IAT at the specified value?

-39°C (-38°F)

Go to Step 6

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C2 located on the opposite side of the manufacturers logo. Refer to Powertrain Control Module Replacement .
  3. Check the IAT signal circuit for a short to a ground. Refer to Testing for Short to Ground in Wiring Systems.
  4. If you find the IAT sensor signal circuit is grounded, repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the IAT signal circuit grounded?

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Go to Step 8

Go to Step 7

6

Replace the IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

Is the action complete?

--

Go to Step 8

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7

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 8

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8

  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

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Go to Step 9

Go to Step 2

9

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK