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 Temperature

Circuit | Normal Range | Short to Ground | Open | Short to Voltage
--- | --- | --- | --- | ---
IAT Sensor Signal | -39 to +120°C (-38 to +248°F) | 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 supplies a ground to the low reference circuit.

### Conditions for Running the DTC

#### P0112

• | DTCs P0116, P0117, P0118, P0128, P0502, P0503 are not set.

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

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

• | This DTC runs continuously within the enabling conditions.

#### P0113

• | DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0128, P0502, P0503 are not set.

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

• | The ECT is greater 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 greater than 149°C (300°F) for greater than 5 seconds.

#### P0113

The ECM detects that the IAT is less 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 elements.

• | 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.

• | An IAT sensor signal circuit that is shorted to the MAF sensor ignition circuit can cause a DTC P0113 to set.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Controls Connector End Views

• | Engine Control Module 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

• | Scan Tool Data List

• | Scan Tool Output Controls

• | Scan Tool Snapshot Procedure

### Circuit/System Verification

• | If the ignition has been OFF for 8 hours or greater, the IAT and the ECT should be within 15°C (27°F) of each other and also the ambient temperature. Ignition ON, observe the scan tool Start-up ECT and Start-up IAT Sensor parameters. Compare those sensor parameters to each other and also to the ambient temperature to determine if the IAT sensor is within an acceptable operating range.

• | 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.

### Circuit/System Testing

Important: All electrical components and accessories must be turned OFF and allowed to power down.

1. Ignition OFF, disconnect the MAF/IAT harness connector at the MAF/IAT sensor.
2. Ignition OFF, test for less than 5 ohms of resistance 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 less than -39°C (-38°F).

⇒ | If greater 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 greater than 149°C (300°F).

⇒ | If less 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 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 vs Resistance table. Refer to Temperature Versus Resistance .

### 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