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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1997 🢒 Firefly (Canada) 🢒 DTC 🢒 DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage

Schematic Reference: Engine Controls Schematics

Circuit Description

The intake air temperature (IAT) sensor is a thermistor. A thermistor is a resistor whose value varies with temperature. The IAT sensor's resistance is high when the air temperature is cold, and the IAT sensor's resistance is low when the air temperature is warm. The IAT sensor is wired in series with a fixed resistor in the powertrain control module (PCM). The PCM applies 5 volts to the IAT sensor. The PCM monitors the voltage across the IAT sensor and converts the voltage into a temperature reading. The PCM will receive a high voltage input when the air temperature is cold. The PCM will receive a low voltage input when the air temperature is warm.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC
    • The IAT sensor signal voltage indicates that the intake air temperature is greater than 119°C (246°F).
    • The above condition is present for at least 0.5 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL).
    • The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.
    • The PCM enters the Fail-Safe Function and assumes the intake air temperature is 20°C (68°F) while stopping idle speed feedback control.

Conditions for Clearing the MIL/DTC
    • The MIL turns OFF after three consecutively passing trips without a fault present.
    • A History DTC clears after 40 consecutive warm-up cycles without a fault.
    • Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC.

Diagnostic Aids

Check for a faulty electrical connection to the PCM.

Use the Temperature vs Resistance table in order to check the IAT sensor at various temperature levels and evaluate the possibility of a shifted (incorrectly calibrated) sensor. A shifted sensor could result in a driveability complaint. Refer to Temperature vs Resistance .

An intermittent malfunction may be caused by a fault in the IAT sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:

    • Backed out terminals.
    • Improper mating of terminals.
    • Broken electrical connector locks.
    • Improperly formed or damaged terminals.
    • Faulty terminal to wire connections.
    • Physical damage to the wiring harness.
    • A broken wire inside the insulation.
    • Corrosion of electrical connections, splices, or terminals.

If a DTC P0112 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. This step checks the current IAT sensor reading.

    3.

  3. This step determines if the fault is present.

    4.

  4. This step determines if the fault is caused by a shorted signal return circuit or by a malfunctioning IAT sensor.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Turn ON the ignition, leaving the engine OFF.
  2. Install a scan tool.
  3. Observe the IAT parameter on the scan tool data list.

Is the IAT display at or greater than the specified value?

119°C (246°F)

Go to Step 4

Go to Step 3

3

  1. Turn ON the ignition, leaving the engine OFF.
  2. Clear the scan tool information.
  3. Operate the vehicle within the Freeze Frame conditions as noted.

Is a DTC P0112 set?

--

Go to Step 4

Go to Diagnostic Aids

4

  1. Disconnect the IAT sensor electrical connector.
  2. Observe the IAT parameter on the scan tool.

Is the IAT display at or below the specified value?

-40°C (-40°F)

Go to Step 7

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the PCM electrical connectors.
  3. Check the IAT sensor signal (input) circuit for a short to ground

Is the IAT sensor signal circuit shorted to ground?

--

Go to Step 8

Go to Step 6

6
  1. Check the IAT sensor ground circuit for a short to voltage.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 10

Go to Step 9

7

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

Is the action complete?

--

Go to Step 10

--

8

Repair the IAT sensor signal (input) circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 10

--

9

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 10

--

10
  1. Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
  2. Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on the scan tool?

--

Go to the Applicable DTC Table

System OK