GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD (LPG) 🢒 DTC 🢒 DTC P0112

Circuit Description

The intake air temperature (IAT) sensor is a thermistor. The IAT thermistor has high resistance when cold and low resistance when hot. The powertrain control module (PCM) supplies about 5 volts on the IAT signal circuit. The PCM also supplies a ground circuit to the IAT sensor. When IAT resistance is high the IAT signal voltage remains near the supplied 5 volts. As the IAT sensor warms and resistance drops, more signal circuit voltage is pulled lower to the sensor ground. The PCM and the Alternative Fuels ECM monitor the IAT signal circuit voltage in order to determine the temperature of the air entering the engine.

This DTC sets when the IAT signal circuit voltage is below the normal operating range of the sensor.

Conditions for Running the DTC
    • The engine is operating on alternative fuel.
    • The engine has been operating for greater than 1.5 minutes.
    • The vehicle speed is greater than 1.6 km/h (1 mph).

Conditions for Setting the DTC

The Alternative Fuels ECM monitors an IAT sensor signal voltage of less than 0.019 volts for at least 5 seconds continuously.

Action Taken When the DTC Sets

    • A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History.
    • The Alternative Fuels ECM will illuminate the MIL and store the DTC as History after 2 consecutive drive trips that the diagnostic runs and fails.
    • The Alternative Fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data.

Conditions for Clearing the MIL/DTC

    • The Last Test Failed status will clear when the DTC runs and passes.
    • The Alternative Fuels ECM will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes.
    • The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC.
    • All DTC Information can be cleared with a scan tool.

Diagnostic Aids

Test Description

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

  1. This step determines if the condition is present.

    2.

  2. This step determines if the IAT sensor is shorted.

    3.

  3. This step determines if a short is present in the wiring harness.

    4.

  4. This step determines if the PCM or the Alternative Fuels ECM is the cause of the shorted condition.

    5.

  5. This step determines if an open circuit condition is present between the PCM and the signal circuit splice.

    If an open condition exists in this circuit the PCM will indicate a high signal voltage, while the Alternative Fuels ECM will indicate low signal voltage.

Step

Action

Value(s)

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Alternative Fuels (Engine Controls)

2

  1. Observe the Freeze Frame and/or the Failure records data for this DTC.
  2. Turn OFF the ignition for 30  seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You also may operate the vehicle within the conditions that you observed from the Freeze Frame and/or the Failure Records data.
  5. Observe the Diagnostic Trouble Code (DTC) Information from the following control modules with a scan tool:
    6. • Alternative Fuels ECM
    • PCM

Does the DTC fail this ignition cycle?

--

Go to Step 3

Go to Intermittent Conditions

3
  1. With a scan tool, establish communication with the powertrain control module (PCM).
  2. Observe the IAT Sensor data parameter.

Does the IAT sensor data parameter indicate IAT temperature warmer than the specified value?

138°C (280°F)

Go to Step 4

Go to Step 7

4

Disconnect the IAT sensor.

Does the IAT sensor data parameter indicate IAT temperature warmer than the specified value?

138°C (280°F)

Go to Step 5

Go to Step 8

5

  1. Turn the ignition OFF.
  2. Disconnect the PCM connector C2. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.
  3. Disconnect the Alternative Fuels ECM connector C002. Refer to Alternative Fuels Engine Control Module Replacement .
  4. Test the IAT signal circuit for continuity to engine ground and also to the sensor ground circuit with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 6

6

  1. Connect the PCM connector C2.
  2. Leave the Alternative Fuels ECM connector disconnected.
  3. Turn the ignition ON, with the engine OFF.
  4. With the IAT sensor connector disconnected, observe the PCM IAT Sensor data parameter.

Does the IAT sensor data parameter indicate IAT temperature warmer than the specified value?

138°C (280°F)

Go to Step 9

Go to Step 10

7

  1. Inspect the signal circuit between the circuit splice and the PCM connector for the following conditions:
    2. • An open
    • High resistance
    • Poor terminal contact
  2. Repair wiring or terminals as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

138°C (280°F)

Go to Step 11

Go to Step 10

8

Replace the IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement in Engine Controls in the C/K Pickup Service Manual.

Did you complete the replacement?

--

Go to Step 11

--

9

Important: KL6 models require a switchover to gasoline with a scan tool in order to perform the Crankshaft Position Variation Learn Procedure.

KL8 models do not require the Crankshaft Position Variation Learn Procedure.

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.

Did you complete the replacement?

--

Go to Step 11

--

10

Replace the Alternative Fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 11

--

11
  1. Use the scan tool in order to clear the DTCs from the following control modules:
    2. • Alternative Fuels ECM
    • PCM
  2. Turn OFF the ignition for 30 seconds.
  3. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 12

Go to Step 2

12

With a scan tool, select Capture Info in order to observe the stored information.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK