For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
IAT Sensor Signal | P0112 | P0111, P0113 | P0113¹ | P0111¹
Low Reference | P0101, P0103 | P0111, P0113 | P0113² | P0101, P0111
¹ Sensor damage may occur if the circuit is shorted to B+. ² Internal ECM damage may occur if the circuit is shorted to B+.

### Typical Scan Tool Data

#### Intake Air Temperature Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Running Condition: The engine is running in closed loop. Parameter Normal Range: -40 to +135°C (-40 to +275°F), which varies with ambient temperature.
IAT Sensor Signal | 135°C (275°F) | -40°C (-40°F) | -40°C (-40°F)¹
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)¹
¹ Internal ECM or sensor damage may occur if the circuit is shorted to B+.

### Circuit Description

The intake air temperature (IAT) sensor is an integral part of the mass air flow (MAF) sensor. The IAT sensor is a variable resistor that measures the temperature of the intake air. The engine control module (ECM) supplies 5 volts to the IAT signal circuit and supplies a ground to the low reference circuit. If the ECM detects a low IAT signal voltage, which is a high temperature indication, this DTC sets.

The following table illustrates the difference between temperature, resistance, and voltage:

IAT | IAT Resistance | IAT Signal Voltage
--- | --- | ---
Cold | High | High
Warm | Low | Low

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage

### Conditions for Running the DTC

• | The engine is running for more than 18 seconds.

• | The engine is idling for more than 10 seconds.

• | The ECM detects that the intake air temperature is less than -42°C, the lowest temperature of the scan tool is limited to -40°C (-40°F) so the diagnostic procedure uses -39°C (-38°F) to determine if there is an IAT condition.

• | The intake air temperature (IAT) value change is less than 3°C (5.4°F).

• | The air flow coming into the engine has accumulated to more than 1,000 grams.

• | DTC P0112 runs continuously once the above conditions are met for 2 seconds.

### Conditions for Setting the DTC

The ECM detects that the intake air temperature is more than 132°C (270°F) for more than 4 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 4 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

• | Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

• | The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Front of Vehicle/Engine Compartment Component Views.

• | Use the Temperature vs Resistance table in order to test the IAT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in a driveability condition. If the engine has sat overnight, the intake air temperature and the engine coolant temperature values should display within a few degrees. If the temperature is not within 3°C (5°F), refer to Temperature Versus Resistance - Intake Air Temperature Sensor.

• | For an intermittent condition, refer to Intermittent Conditions.

### Test Description

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

1. This step determines that a condition exists. If the temperature is more than the specified value, test for a condition in the circuits of the IAT sensor.

2. This step isolates the condition. If the temperature is less than the specified value, the ECM and the signal circuit of the IAT sensor are OK.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Component Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Turn the ignition switch to ON position, with the engine OFF.
2. Observe the IAT sensor parameter with a scan tool.

Is the temperature more than the specified value?

132°C (270°F)

Go to Step 4

Go to Step 3

3 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Disconnect the mass air flow (MAF)/intake air temperature (IAT) sensor. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement.
2. Turn the ignition switch to ON position, with the engine OFF.
3. Observe the IAT sensor parameter with a scan tool.

Is the temperature less than the specified value?

-38°C (-36°F)

Go to Step 6

Go to Step 5

5 |

1. Turn OFF the ignition.
2. Disconnect the engine control module (ECM).
3. Test the signal circuit of the IAT sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

6 | Replace the IAT sensor. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement. Did you complete the replacement? | -- | Go to Step 8 | --
7 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 8 | --
8 |

1. Clear any DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 9

9 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK