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 P1111: Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage
DTC P1112: Intake Air Temperature (IAT) Sensor Circuit Intermittent Low Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
IAT Sensor Signal | P0112, P1112 | P0113, P1111 | P0113, P1111¹ | P0110, P0111
Low Reference | -- | P0113, P1111 | P0113, P1111¹ | P0110, P0111
¹ Internal ECM or sensor damage may occur if the circuit is shorted to B+.

### 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)¹
Low Reference | -- | 20°C (68°F) | --
¹ Internal ECM or sensor damage may occur if the circuit is shorted to B+.

### 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

#### P1111

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

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

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

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

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

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

#### P1112

• | DTC P0502 is not set.

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

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

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

### Conditions for Setting the DTC

#### P1111

The ECM detects that the IAT sensor parameter is less than -38°C (-36°F) for more than 3 seconds intermittently.

#### P1112

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

### Action Taken When the DTC Sets

DTCs P1111 and P1112 are Type C DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P1111 and P1112 are Type C DTCs.

### 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. Verify that DTCs P0112 or P0113 are not set.

⇒ | If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

2. Operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. DTC P1111 or P1112 should not set.
3. 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 List.

### Circuit/System Testing

1. Start the engine. Observe the intake air temperature (IAT) sensor parameter while moving the harness connector of the sensor. The IAT sensor parameter should not change abruptly.

⇒ | If the IAT sensor parameter changes abruptly, repair the harness connector of the IAT sensor.

2. Engine running, observe the IAT sensor parameter while moving the harness connector of the ECM. The IAT sensor parameter should not change abruptly.

⇒ | If the IAT sensor parameter changes abruptly, repair the harness connector of the ECM.

3. Engine running, observe the IAT sensor parameter while moving the wiring harness between the sensor and ECM. The IAT sensor parameter should not change abruptly.

⇒ | If the IAT sensor parameter changes abruptly, repair the wiring harness.

### 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