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 Descriptor

DTC P0112 00: Intake Air Temperature Sensor Circuit Low Voltage
DTC P0113 00: Intake Air Temperature Sensor Circuit High Voltage

### Circuit/System Description

The intake air temperature (IAT) sensor 1 is an integral part of the mass air flow (MAF) sensor. The IAT sensor is a variable resistor that measures the temperature of the intake air. The engine control module (ECM) supplies 5 V to the IAT signal circuit and supplies a ground to the 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

• | The ignition is ON or the engine is running.

• | The ignition voltage is greater than 8.5 V.

• | The DTCs run continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P0112

The ECM detects that an IAT 1 circuit is shorted to ground.

#### P0113

The ECM detects that an IAT 1 circuit is open or shorted to voltage.

### 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 has sat overnight, the IAT sensor and the engine coolant temperature (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 set a DTC.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component 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

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. DTC 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 B75 Mass Air Flow (MAF) Sensor.
2. Test for less than 5 Ω of resistance between the low reference circuit terminal 1 and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance, or for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

3. Ignition ON, test for 4.8-5.2 V between the IAT signal circuit terminal 3 and ground.

⇒ | If less than the specified range, test the signal circuit for an open or a short to ground. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

4. If all circuits test normal, test or replace the B75 Mass Air Flow (MAF) Sensor.

### Component Testing

#### Static Test

Test and record the resistance between the signal circuit terminal 3 and the low reference circuit terminal 1 at various ambient temperatures. Compare those measurements to the Temperature Versus Resistance table and verify that the resistance is within 5% of the specification.

⇒ | If not within the specified range, replace the B75 Mass Air Flow (MAF) Sensor

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Mass Airflow Sensor with Intake Air Temperature Sensor Replacement

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