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 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**

--

* Sensor damage may occur if the circuit is shorted to B+.

** Internal ECM 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

129°C (264°F), 0.0 Volts

-40°C (-40°F), 5.0 Volts

-40°C (-40°F), 5.0 Volts

Low Reference

--

-40°C (-40°F), 5.0 Volts

-40°C (-40°F), 5.0 Volts*

* Internal ECM 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

    • The ignition is ON or the engine is running.
    •  The DTCs runs continuously once the above condition is met.

Conditions for Setting the DTC

P0112

The ECM detects that the IAT sensor voltage is less than 0.01 volt for more than 3 seconds.

P0113

The ECM detects that the IAT sensor voltage is greater than 4.99 volts for more than 3 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 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 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 1 minute, observe the DTC information with a scan tool. DTCs P0112 and 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.
  3. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  4. Ignition ON, verify the scan tool IAT sensor parameter is at -40°C (-40°F).
  5. If greater than the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.
  6. 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 129°C (264°F).
  7. 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.
  8. If all circuits test normal, test or replace the IAT sensor.

Component Testing

  1. Ignition OFF, disconnect the harness connector at the 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 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 ECM replacement, setup, and programming