GM Service Manual Online
For 1990-2009 cars only

Object Number: 185072  Size: LF
Engine Controls Components
Engine Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The intake air temperature (IAT) sensor is a thermistor that controls signal voltage to the PCM. When the air is cold, the sensor resistance is high, therefore the PCM will see a high signal voltage. As air warms, sensor resistance becomes less and voltage drops.

Conditions for Running the DTC

    • The PCM performs this DTC diagnostic continuously.
    • The engine coolant temperature is less than 42.5°C (109°F).

Conditions for Setting the DTC

    • The Intake air temperature is more than or equal to 151°C (303°F).
    • All of the diagnostic set conditions were met for 2 seconds.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The PCM will turn the MIL off after 3 consecutive trips without a fault condition.
    • A history DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
    • The scan tool Clear Info function was used.

Diagnostic Aids

Check harness routing for a potential short to ground in the signal circuit. Refer to Symptoms . The scan tool displays intake air temperature in degrees centigrade. A skewed sensor could result in poor driveability complaints. Refer to Temperature vs Resistance .

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. This step determines if P0112 is a hard failure or an intermittent condition.

  2. This test will determine if the PCM can recognized an open sensor.

  3. This step will determine if the problem is a short to ground or a malfunctioning PCM.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing any DTCs, use the scan tool Capture Info to save freeze frame and failure records for reference, as the scan tool loses data when using the Clear Info function.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Connect a scan tool.
  2. Start the engine.
  3. Monitor the IAT display on scan tool.

Is the IAT display greater than or equal to the specified value?

151°C (303°F)

Go to Step 3

Go to Step 5

3

  1. Turn the engine OFF.
  2. Turn the ignition ON leaving the engine OFF.
  3. Disconnect the IAT sensor connector.

Does the IAT display a temperature colder than or equal to the specified value?

-30°C (-22°F)

Go to Step 7

Go to Step 4

4

  1. Turn the ignition OFF.
  2. Disconnect the PCM connector with the IAT signal circuit.
  3. Using the J 39200 DMM, measure the resistance across the IAT harness connector.

Is the resistance at the specified value?

Go to Step 8

Go to Step 6

5

The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs were stored, refer to those table(s).

Are any additional DTCs stored?

--

Go to the Applicable DTC Table

Go to Diagnostic Aids

6

Repair the short to ground in the IAT signal circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 9

--

7

Replace the IAT sensor. Refer to IAT Sensor Replacement .

Is the action complete?

--

Go to Step 9

--

8

Replace the PCM.

Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 9

--

9

  1. Using the scan tool, clear the DTCs.
  2. Start the engine .
  3. Allow the engine to idle at normal operating temperature.
  4. Select DTC and the Specific DTC function.
  5. Enter the DTC number which was set.
  6. Operate the vehicle, within the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

--

Go to Step 10

Go to Step 2

10

Does the scan tool display any additional undiagnosed DTCs?

--

Go to the Applicable DTC Table

System OK