GM Service Manual Online
For 1990-2009 cars only

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 provide 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

168°C (334°F),

20°C (68°F),

20°C (68°F),

Low Reference

--

20°C (68°F),

--

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.
    • The vehicle speed is greater than 50 km/h (31 mph).
    • This DTC runs continuously when the above conditions are met.

P0113

    • DTCs P0117, P0118, and P0502 are not set.
    • The engine airflow is less than 15 g/s.
    • The vehicle speed is less than 25 km/h (15 mph).
    • The engine run time is more than 120 seconds.
    • The ECT sensor is greater than 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 more than 149°C (300°F) for 10 seconds.

P0113

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

Action Taken When the DTC Sets

DTC P0112 and P0113 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTC 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

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

  3. Ignition ON, verify that the IAT sensor parameter is at -40°C (-40°F).
  4. If greater than -40°C (-40°F), test the signal circuit of the IAT sensor for a short to ground. If the circuit/connections test normal, replace the engine control module (ECM).
  5. Test for less than 0.5 volt between the low reference circuit of the IAT sensor and the negative terminal of the battery.
  6. If greater than 0.5 volt, test the low reference circuit of the IAT sensor for a short to voltage. If the circuit/connections test normal, replace the ECM.
  7. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit of the IAT sensor and the negative terminal of the battery.
  8. If greater than 5 ohms, test the low reference circuit of the IAT sensor for an open/high resistance. If the circuit/connections test 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.

  9. Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the IAT sensor and verify the IAT sensor parameter is greater than 128°C (262°F).
  10. If less than 128°C (262°F), test the signal circuit of the IAT sensor for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.
  11. If all circuits/connections test normal, test or replace the IAT sensor.

Component Testing

  1. Ignition OFF, disconnect the harness connector of the intake air temperature (IAT) sensor.
  2. Important: A thermometer can be used to test the sensor off the vehicle.

  3. 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.
  4. 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