For 1990-2009 cars

### Circuit Description

The intake air temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The powertrain control module (PCM) applies 5 volts through a pull up resistor. When the intake air is cold, the sensor resistance is high and the PCM will monitor a high signal voltage on the IAT sensor signal circuit. As the intake air warms, the sensor resistance becomes lower causing the PCM to monitor a lower voltage. If the PCM detects an excessively low IAT sensor signal voltage, high temperature indicated, DTC P0112 will set.

### Conditions for Running the DTC

• | DTCs P0101, P0102, P0103, P0117, P0118, P0125, P0128, P0502, P0503, P1114, or P1115 are not set.

• | The engine has been running for more than 10 seconds.

• | The vehicle speed is more than 40 km/h (25 mph).

### Conditions for Setting the DTC

• | The IAT signal voltage indicates an intake air temperature that is more than 135°C (275°F).

• | The above conditions are present for at least 20 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.

### Test Description

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

1. Verifies that the fault is present.

2. If DTC P0112 can be repeated only by duplicating the Failure Records conditions, refer to the Temperature vs Resistance table. The table may be used to test the IAT sensor at various temperatures in order to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the IAT sensor. If the IAT sensor appears to be OK, the fault is intermittent refer to Diagnostic Aids.

#### DTC P0112 IAT Sensor 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 |

1. Turn ON the ignition, with the engine OFF.
2. With a scan tool, observe the IAT parameter.

Does the scan tool indicate the IAT parameter is more than specified value?

135°C (275°F)

Go to Step 4

Go to Step 3

3 |

1. With a scan tool, review and record the Failure Records data.
2. Operate the vehicle within the Failure Records conditions as noted.

Does the scan tool indicate DTC P0112 failed this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4 |

1. Turn OFF the ignition.
2. Disconnect the IAT sensor.
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, observe the IAT parameter.

Does the scan tool indicate the IAT parameter is less than the specified value?

-37°C (-35°F)

Go to Step 6

Go to Step 5

5 |

1. Turn OFF the ignition.
2. Test the signal circuit of the IAT sensor for a short to ground. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

6 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 8 | --
7 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 8 | --
8 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Failure Record conditions as noted.

Does the DTC reset?

--

Go to Step 2

System OK