For 1990-2009 cars
Engine Controls Components
Cell 23: Engine Data Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views With EGR
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The intake air temperature (IAT) sensor uses a thermistor 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, therefore the IAT signal voltage will be high. If the intake air is warm, resistance is low, therefore the IAT signal voltage will be low.

### Conditions for Running the DTC

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

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

### Conditions for Setting the DTC

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

### Action Taken When the DTC Sets (With EGR)

• | The Malfunction Indicator Lamp (MIL) will illuminate.

• | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

• | A history DTC is stored.

• | Coolant fan turns ON.

• | The PCM will default to 60°C (140°F) for intake air temperature. The scan tool will not the show the defaulted value.

### Action Taken When the DTC Sets (Without EGR)

• | The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with fault active.

• | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

• | A history DTC is stored.

• | Coolant fan turns ON.

• | The PCM will default to 60°C (140°F) for intake air temperature. The scan tool will not the show the defaulted value.

### Conditions for Clearing the MIL/DTC

• | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

• | The MIL/DTCs can be cleared by using the scan tool.

### Diagnostic Aids

• | If the vehicle is at 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 Values table to evaluate the possibility of a skewed sensor. Refer to Temperature vs Resistance .

### Test Description

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

1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

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

3. Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming and the Crankshaft Position System Variation Learn for the crankshaft position system variation learn procedure.

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

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 switch leaving the engine OFF.
2. Install a scan tool.

Is the IAT sensor value greater than the specified value?

128°C (262°F)

Go to Step 4

Go to Step 3

3 |

1. Review the Freeze Frame data and record the parameters.
2. Start the engine.
3. Operate the vehicle within the Freeze Frame conditions and Conditions For Running The DTC as specified in the supporting text.

Is the IAT sensor value greater than the specified value?

128°C (262°F)

Go to Step 4

Go to Diagnostic Aids

4 |

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

Is the IAT sensor value below the specified value?

-30°C (-22°F)

Go to Step 5

Go to Step 6

5 |

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

Is the action complete?

--

Go to Step 10

--

6 |

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

Does the test light illuminate?

--

Go to Step 7

Go to Step 9

7 |

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

Does the test light 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. Is the action complete? | -- | Go to Step 10 | --
9 |

1. Check for a poor electrical terminal connection at the PCM.
2. If the electrical connection is OK, replace the PCM. refer to the Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 10

--

10 |

1. Using the scan tool, clear the DTCs.
2. Start the engine.
3. Idle the engine at the normal operating temperature.
4. Operate the vehicle within the conditions for running this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 11

Go to Step 2

11 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to applicable DTC table | System OK