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 | P0111
Low Reference | -- | -- | P0113 | -- | --

### Typical Scan Tool Data

#### Intake Air Temperature Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: The ignition is ON or the engine is running. Parameter Normal Range: -39 to +120°C (-38 to +248°F)
IAT Sensor Signal | 149°C (300° F) | -40°C (-40°F) | -40°C (-40°F)
IAT Low Reference | -- | -40°C (-40°F) | --

### Circuit Description

The intake air temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The intake air temperature (IAT) sensor measures the temperature of the air entering the engine. The engine control module (ECM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the IAT signal circuit.

### Conditions for Running the DTC

#### P0112

• | DTCs P0116, P0117, P0118, P0128, P0608, and P0609 are not set.

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

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

• | The vehicle speed exceeds 0 km/h.

• | DTC P0112 runs continuously when the above conditions are met.

#### P0113

• | DTC P0101, P0102, P0103, P0116, P0117, P0118, P0128, P0608 or P0609 are not set.

• | The ECT sensor values is more than -40°C (-40°F).

• | The mass air flow (MAF) sensor is less than 512 g/s.

• | The vehicle speed is less than 512 km/h.

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

• | DTC P0113 runs continuously when the above conditions are met.

### Conditions for Setting the DTC

#### P0112

• | The ECM detects that the IAT sensor resistance of the HO2S is less than 45 ohms, approximately 150°C (302°F).

• | It occurs 50 times during the 63 tests.

• | DTC P0102 sets when the above conditions are met.

#### P0113

• | The ECM detects that the IAT sensor resistance of the HO2S is more than 163,000 ohms, approximately -60°C (-76°F).

• | It occurs 50 times during the 63 tests.

• | DTC P0113 sets when the above conditions are met.

### Action Taken When the DTC Sets

DTCs P0112 and P0113 are Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0112 and P0113 are Type B DTCs.

### Diagnostic Aids

If the engine is cold, with the 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 MAF sensor heating elements.

### 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

Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Engine Control Module Scan Tool Information

### Circuit/System Verification

• | Observe the IAT sensor parameter with a scan tool when the engine is running. The reading should be -39 to +120°C (-38 to +248°F) depending on the current ambient temperature and the vehicle operating conditions.

| Important: Perform this verification procedure only when the ignition has been OFF for 8 hours or more.

• | The IAT will begin to warm up once the ignition key is turned ON.

• | Turn the ignition ON, observe the scan tool IAT Sensor and ECT Sensor parameters. The reading of sensor parameter and ambient temperature should be less than 15°C (27°F).

### Circuit/System Testing

1. Turn the ignition OFF, disconnect the harness connector at the MAF/IAT sensor.
2. Turn the ignition OFF, allow sufficient time for the control module to power down. Test for less than 5 ohms between the low reference circuit terminal D and ground.

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

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

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

Important: If the condition of a short to voltage is found on the IAT signal circuit exist, the 3-amp fuse in the jumper wire will open.

4. Install a 3-amp fused jumper wire between the signal circuit terminal E and ground. Verify the scan tool IAT sensor parameter is greater than 149°C (300°F).

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

5. If all circuits test normal, test the MAF/IAT sensor. Refer to Component Testing.

### Component Testing

Measure the resistance of the IAT sensor and then compare those measurements with the Temperature vs Resistance. Refer to Temperature Versus Resistance .

⇒ | If the resistance is not within the range 9 percent listed in the Temperature vs. Resistance, replace the IAT sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Mass Airflow Sensor/Intake Air Temperature Sensor Replacement

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