For 1990-2009 cars

### Circuit Description

The intake air temperature (IAT) sensor uses a thermistor in order to control the signal voltage to the powertrain control module (PCM). The PCM supplies a 5-volt reference and a ground to the sensor. When the air is cold the resistance is high, and the IAT signal voltage will be high. If the intake air is warm, the resistance is low, and the IAT signal voltage will be low.

### Conditions for Running the DTC

• | The engine run time is more than 320 seconds.

• | The vehicle speed sensor indicates that vehicle speed is more than 24 km/h (15 mph).

• | DTCs P0117, P0118, P0125, P0502, or P0503 are not set.

### Conditions for Setting the DTC

The IAT sensor signal voltage indicates that the intake air temperature is more than 128°C (262°F) for 3.125 seconds.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• | 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

• | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

• | If the vehicle is at the ambient temperature, compare the IAT sensor to the ECT sensor. The IAT sensor and the ECT sensor should be relatively close to each other.

• | Use the Temperature vs. Resistance table in order to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance .

• | For an intermittent, refer to Intermittent Conditions .

### Test Description

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

1. This step simulates a DTC P0113 condition. If the scan tool displays the specified value, the IAT signal circuit and the PCM are OK.

2. The replacement PCM must be programmed and the Crankshaft Position System Variation Learn procedure must be preformed.

#### DTC P0112-Intake Air Temperature (IAT) Circuit-Low Voltage

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Turn ON the ignition, leaving the engine OFF. Is the IAT more than the specified value? | 128°C (262°F) | Go to Step 4 | Go to Step 3
3 |

1. Review and record the Freeze Frame data.
2. Operate the vehicle within the Freeze Frame conditions and the Conditions for Running the DTC, as specified in the supporting text.

Is the IAT more than the specified value?

128°C (262°F)

Go to Step 4

Go to Diagnostic Aids

4 |

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

Is the IAT less than the specified value?

-30°C (-22°F)

Go to Step 5

Go to Step 6

5 |

1. Turn OFF the ignition.
2. Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement .

Did you complete the repair?

--

Go to Step 11

--

6 |

1. Turn OFF the ignition.
2. Connect a test lamp to B+.
3. Probe the IAT sensor signal circuit at the IAT sensor connector.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 9

7 |

1. Turn OFF the ignition.
2. Disconnect the PCM connector.
3. Connect a test lamp to B+.
4. Probe the IAT sensor signal circuit at the IAT sensor connector.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 9

8 | Repair the short to ground in the IAT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 11 | --
9 | Inspect for a poor connection at the PCM. If a problem is found, repair as necessary. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the repair? | -- | Go to Step 11 | --
11 |

1. Use a 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?

--

Go to Step 12

Go to Step 2

12 | 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