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.

### DTC Descriptors

DTC P0112: Intake Air Temperature (IAT) Sensor Circuit Low Voltage
DTC P0113: Intake Air Temperature (IAT) Sensor Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
IAT Sensor Signal | P0112 | P0113 | P0113 | P0113 | --
Low Reference | -- | P0113 | P0113 | P0113 | --

### Typical Scan Tool Data

#### IAT Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine Running Parameter Normal Range: -39 to +120°C (-38 to +248°F) depending on the ambient temperature
IAT Sensor Signal | 150°C (302°F) | -40°C (-40°F) | -40°C (-40°F)
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)

### Circuit/System Description

The intake air temperature (IAT) sensor is a variable resistor that measures the temperature of the air entering the engine. The engine control module (ECM) supplies 5 volts to the IAT sensor signal circuit and a ground for the low reference circuit.

### Conditions for Running the DTC

#### P0112

• | DTC P0116, P0117, P0118, P0128, P0502, or P0503 is not set.

• | The engine is running for greater than 10 seconds.

• | The engine coolant temperature (ECT) is colder than 150°C (302°F).

• | This DTC runs continuously within the enabling conditions.

#### P0113

• | DTC P0101, P0102, P0103, P0116, P0117, P0118, P0128, P0502, or P0503 is not set.

• | The engine is running for greater than 10 seconds.

• | The ECT is warmer than -40°C (-40°F).

• | This DTC runs continuously within the enabling conditions.

### Conditions for Setting the DTC

#### P0112

The ECM detects that the IAT is warmer than 149°C (300°F) for greater than 5 seconds.

#### P0113

The ECM detects that the IAT is colder than -39°C (-38°F) for greater than 5 seconds.

### Action Taken When the DTC Sets

DTCs P0112 and P0113 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0112 and P0113 are Type B DTCs.

### Diagnostic Aids

• | If the engine is cold, then at ignition ON, a properly functioning IAT sensor will gradually increase the scan tool IAT Sensor parameter. This is due to the heat that is generated by the mass air flow (MAF) sensor heating element.

• | Depending on the ambient temperature, an IAT sensor signal circuit or low reference circuit that is shorted to the MAF sensor signal circuit can cause a DTC P0113 to set. This condition causes a rapid fluctuation in the IAT Sensor parameter.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition OFF for 8 hours or greater.
2. Ignition ON, observe the scan tool IAT Sensor and ECT Sensor parameters. The IAT, ECT, and ambient temperatures should be within 15°C (27°F) of each other.
3. Engine running, observe the scan tool IAT Sensor parameter. The reading should be between -39 to +120°C (-38 to +248°F) depending on the current ambient temperature and the vehicle operating conditions.
4. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the MAF/IAT sensor.
2. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal D and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, verify the scan tool IAT Sensor parameter is colder than -39°C (-38°F).

⇒ | If warmer than the specified range, test the signal circuit terminal E for a short to ground. If the circuit tests normal, replace the ECM.

4. Install a 3A fused jumper wire between the signal circuit terminal E and a good ground. Verify the scan tool IAT Sensor parameter is warmer than 149°C (300°F).

⇒ | If colder than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal replace the ECM.

5. If the circuits test normal, test or replace the IAT sensor.

### Component Testing

Measure and record the resistance of the IAT sensor at various ambient temperatures, then compare those measurements to the Temperature Versus Resistance table.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Mass Airflow Sensor Replacement

• | Control Module References for ECM replacement, setup, and programming