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

### Typical Scan Tool Data

#### IAT Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine operating in Closed Loop Parameter Normal Range: Varies with ambient temperature
IAT Sensor Signal | 130°C (266°F) | 20°C (68°F) | 20°C (68°F)
Low Reference | -- | 20°C (68°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 IAT sensor has a signal circuit and a low reference circuit. The engine control module (ECM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit.

The following table illustrates the difference between temperature, resistance, and voltage:

IAT | IAT Resistance | IAT Signal Voltage
--- | --- | ---
Cold | High | High
Warm | Low | Low

### Conditions for Running the DTC

#### P0112

• | DTC P0502 is not set.

• | The engine run time is greater than 120 seconds.

• | The vehicle speed is greater than 50 km/h (31 mph).

• | This DTC runs continuously once the above conditions are met.

#### P0113

• | DTCs P0117, P0118, and P0502 are not set.

• | The engine run time is greater than 120 seconds.

• | The engine coolant temperature is greater than 70°C (158°F).

• | The calculated air flow is less than 15 g/s.

• | The vehicle speed is less than 25 km/h (16 mph).

• | The engine coolant temperature (ECT) is above between 70°C (158°F).

• | This DTC runs continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P0112

The ECM detects that the IAT sensor is greater than 149°C (300°F) for greater than 20 seconds.

#### P0113

The ECM detects that the IAT sensor parameter is less than -38°C (-36°F) for greater than 120 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 vehicle has set overnight, the IAT sensor and the ECT sensor values should display within 3°C (5°F).

• | High resistance on either the IAT sensor signal circuit or the IAT sensor low reference circuit may not set a DTC.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### 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. Engine running for 4 minutes, observe the DTC information with a scan tool. DTCs P0112 or P0113 should not set.
2. 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 IAT sensor.
2. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal 2 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.

Important: The DTCs must be cleared or a temperature of 20°C (68°F) will be displayed on the scan tool.

3. Verify the scan tool IAT sensor parameter is at -40°C (-40°F).

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

Important: The DTCs must be cleared or a temperature of 20°C (68°F) will be displayed on the scan tool.

4. Install a 3A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. Verify the scan tool IAT sensor parameter is greater than 128°C (262°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 all circuits test normal, test or replace the IAT sensor.

### Component Testing

1. Ignition OFF, disconnect the harness connector at the IAT sensor.

Important: A thermometer can be used to test the sensor off the vehicle.

2. Test the IAT sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance table and verify that the resistance is within 5 percent of the specification.

⇒ | If not within the specified range, replace the IAT sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Intake Air Temperature Sensor Replacement

• | Control Module References for engine control module replacement, setup, and programming