GM Service Manual Online
For 1990-2009 cars only

Object Number: 394149  Size: SF
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Engine Controls Components
Cell 21: Engine Sensors (Utility)
OBD II Symbol Description Notice

Circuit Description

The intake air temperature (IAT) sensor is a thermistor. The control module supplies the IAT sensor a reference voltage on the IAT sensor signal circuit and a ground circuit. When the IAT sensor resistance is high, indicating a cold sensor, the IAT sensor signal voltage remains near the supplied voltage and decreases the signal voltage as the sensor warms. The control module monitors the IAT sensor signal circuit in order to calculate the temperature of the air entering the engine.

This DTC is designed to detect intermittent low voltage signals on the IAT sensor signal circuit.

Conditions for Running the DTC

    • No active VS sensor DTCs
    • The vehicle speed is more than 2 mph (3 km/h)
    • The engine has been running for more than 100 seconds

Conditions for Setting the DTC

The IAT voltage is less than a calibrated voltage for less than 1 second

Action Taken When the DTC Sets

    • The control module stores the DTC in history after the first failure but will not illuminate the malfunction indicator lamp (MIL).
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

    • A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles.
    • A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle.
    • Use the scan tool Clear Information function.

Diagnostic Aids

The IAT sensor indicates the temperature of the ambient air entering the throttle body. The scan tool displays the IAT as volts and temperature. The IAT temperature should read very close to the temperature of the outside air and should rise gradually as the engine warms up and the underhood temperature increases. An intermittent short to ground in the IAT sensor signal circuit could result in a DTC P1112. If the low IAT sensor voltage reading is present, additional sensor circuit voltage codes could be set. Refer to any non-intermittent DTCs that are set. Also, a sensor may become skewed or mis-scaled. The Temperature vs. Resistance Value Table will help to detect a skewed sensor. Refer to Temperature vs Resistance .

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

Important: Be sure to use the same diagnostic test equipment for all measurements

  1. If the IAT sensor circuit voltage is less than 0.25 volts, then the condition is present. Even though DTC P0112 did not set, this DTC is more comprehensive and may aid in diagnosis.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The control module's data is deleted once the Clear Info function is used.

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install the scan tool.
  2. Turn ON the ignition leaving the engine OFF.
  3. Display the IAT sensor voltage.

Is the IAT sensor voltage less than the specified value?

0.25 V

Go to DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the IAT sensor harness connector.
  3. Inspect the IAT sensor harness connector and terminals.

Did you find a problem?

--

Go to Step 6

Go to Step 4

4

  1. Disconnect the VCM C2 and C3 connectors.
  2. Inspect the terminals and connectors.

Did you find a problem?

--

Go to Step 6

Go to Step 5

5

  1. Reconnect the VCM and IAT sensor harness connectors.
  2. Turn ON the ignition leaving the engine OFF.
  3. Check for an intermittent short to ground in the IAT sensor signal circuit while moving the harness in various locations.
  4. Display the IAT sensor voltage while moving the harness.

Did the voltage fluctuate?

--

Go to Step 6

Go to Diagnostic Aids

6

Repair the circuit as necessary. Refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 7

--

7

  1. Using the scan tool, clear the DTCs.
  2. Start the engine.
  3. Allow the engine to idle until the engine reaches normal operating temperature.
  4. Select DTC and the Specific DTC function.
  5. Enter the DTC number which was set.
  6. Operate the vehicle, with the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

--

Go to Step 8

Go to Step 2

8

Does the scan tool display any additional undiagnosed DTCs?

--

Go to the applicable DTC table

System OK