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 | P0110, P0111
Low Reference | -- | P0113 | P0113 | P0110, P0111

### 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 | 141°C (286°F), | -40°C (-40°F) | -40°C (-40°F)¹
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)¹
¹ Internal ECM or sensor damage may occur if the circuit is shorted to B+.

### Circuit 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 more than 120 seconds or the ignition has been off for more than 8 hours before vehicle is started.

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

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

#### P0113

• | DTCs P0106, P0107, P0108, P0117, P0118, and P0502 are not set.

• | The calculated engine airflow is less than 15 g/s.

• | The vehicle speed is less than 25 km/h (15 mph).

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

• | The engine run time is more than 120 seconds, or the ignition has been off for more than 8 hours before vehicle is started.

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

### Conditions for Setting the DTC

#### P0112

The ECM detects that the IAT sensor is more than 149°C (300°F) for more than 10 seconds.

#### P0113

The ECM detects that the IAT sensor parameter is less than -38°C (-36°F) for more than 4 seconds.

### Action Taken When the DTC Sets

DTCs P0112 and P0113 are Type A DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0112 and P0113 are Type A 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

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls 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 Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

1. With the engine idling for 4 minutes, observe the DTC information with a scan tool. DTC P0112 or P0113 should not set.
2. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the IAT sensor.
2. Ignition ON, clear the DTC information with a scan tool.
3. Ignition ON, verify that the IAT sensor parameter is at -40°C (-40°F).

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

4. Test for less than 0.5 volt between the low reference circuit and ground.

⇒ | If greater than the specified value, test the low reference circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.

5. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit and ground.

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

6. Ignition ON, clear the DTC information with a scan tool.
7. Install a 1-amp fused jumper wire between the signal circuit and the low reference circuit. Verify the IAT sensor parameter is greater than 135°C (275°F).

Important: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.

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

8. If all circuits/connections test normal, test or replace the IAT sensor.

### Component Testing

1. Ignition OFF, disconnect the harness connector of 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 the resistance Vs. temperature is not within 5 percent, 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