For 1990-2009 cars
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The Intake Air Temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The PCM applies 5V through a pull-up resistor to the IAT sensor. When the intake air is cold, the sensor resistance is high and the PCM will monitor a high signal voltage on the IAT signal circuit. If the intake air is warm, the sensor resistance is lower causing the PCM to monitor a lower voltage. DTC P0112 will set when the PCM detects an excessively low signal voltage on the intake air temperature sensor signal circuit.

### Conditions for Setting the DTC

• | No active ECT sensor, MAF sensor or VSS DTC present.

• | Engine running for over 30 seconds.

• | Vehicle speed is greater than 25 mph.

• | IAT signal voltage indicates an intake air temperature greater than 139°C (282°F).

• | The above conditions are present for at least 30 seconds.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.

• | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using the scan tool.

### Diagnostic Aids

Check for the following conditions:

• | Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection

• | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving connectors and wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the fault.

If DTC P0112 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set.

### Test Description

The number below refers to the step number on the Diagnostic Table.

1. Verifies that the fault is present.

2. If DTC P0112 can be repeated only by duplicating the Fail Records conditions, refer to the Temperature vs. Resistance Value table. The table may be used to test the IAT sensor at various temperatures 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.

3. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to PCM Replacement and Programming Procedures in Powertrain Control Module (PCM) and Sensors.

#### DTC P0112 IAT Sensor Circuit Low Voltage

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic System Check Performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Ignition ON, observe the Intake Air Temp display on the scan tool Eng 1 data list. Is Intake Air Temp. greater than specified value? | 130°C (266°F) | Go to Step 4 | Go to Step 3
3 |

1. Ignition ON, engine OFF, review and record scan tool Fail Records data.
2. Operate vehicle within Fail Records conditions as noted.
3. Using a scan tool, monitor SPECIFIC DTC info for DTC P0112?

Does scan tool indicate DTC P0112 failed this ignition?

--

Go to Step 4

Refer to Diagnostic Aids

4 |

1. Disconnect IAT Sensor electrical connector.
2. Observe Intake Air Temperature on scan tool.

Is Intake Air Temperature below the specified value?

-30°C (-22°F)

Go to Step 6

Go to Step 5

5 |

1. Ignition OFF.
2. Disconnect the PCM electrical connectors.
3. Check IAT sensor signal circuit for a short to ground.

Is IAT sensor signal circuit shorted to ground?

--

Go to Step 7

Go to Step 8

6 | Replace IAT Sensor. Refer to Intake Air Temperature Sensor Replacement . Is action complete? | -- | Go to Step 9 | --
7 | Repair IAT sensor signal circuit. Is action complete? | -- | Go to Step 9 | --
8 | Replace the PCM. Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | Go to Step 9 | --
9 |

1. Ignition ON, engine OFF, review and record scan tool Fail Records data.
2. Clear DTCs.
3. Operate vehicle within Fail Records conditions as noted.
4. Using a scan tool, monitor SPECIFIC DTC info for DTC P0112?

Does scan tool indicate DTC P0112 failed this ignition?

--

Go to Step 2

Repair complete