GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD (LPG) 🢒 DTC 🢒 DTC P0101

Circuit Description

The mass air flow (MAF) sensor is an air flow meter. The MAF sensor is supplied ignition voltage and a ground. The MAF sensor heats a wire grid or a small wire within the sensor to a predetermined temperature. As inlet air flows across and cools the wire grid, the MAF sensor must increase current flow to the wire grid in order to maintain a constant wire grid temperature. The MAF sensor converts the required wire grid current flow into a frequency signal. The powertrain control module (PCM) and the Alternative Fuels ECM monitor the MAF signal circuit frequency and determine the flow and mass of the air entering the engine.

The PCM and the Alternative Fuels ECM convert the MAF signal circuit frequency into a grams per second value. At idle the MAF sensor will produce a low frequency signal, around 2,000 Hz or 6 grams per second. At wide open throttle the MAF sensor will produce a high frequency signal, around 9,000 Hz or 125 grams per second.

The PCM and the Alternative Fuels ECM monitor the actual MAF sensor air flow rate and compare the actual air flow rate to a calculated air flow rate. The calculated air flow rate is based upon engine speed and barometric pressure (BARO). The PCM and the Alternative Fuels ECM use the MAP sensor in order to determine the BARO when the ignition switch is turned ON and the engine is NOT cranked. This BARO reading may also be updated whenever the engine is operated at wide open throttle.

This DTC sets when the actual MAF sensor air flow rate does not match a calculated air flow rate.

Conditions for Running the DTC
    • The engine is operating on alternative fuel.
    • No Alternative Fuels ECM, ECT, TP, IAT, MAP, or MAF sensor DTCs are set.
    • The engine has been operating for more than 10 seconds.
    • The engine speed is more than 500 RPM.
    • The battery voltage is more than 10 volts.
    • The MAP sensor performance DTC P0106 has run at least once this ignition cycle.

Conditions for Setting the DTC

The Alternative Fuels ECM monitors an actual MAF sensor air flow rate that does not match a calculated air flow rate for at least 5 seconds continuously.

Action Taken When the DTC Sets

The Alternative Fuels ECM will switch-over to gasoline fuel operation. Alternative fuel operation will not be attempted until the next ignition key cycle.

    • The Alternative Fuels ECM will illuminate the MIL and store the DTC as History during 1 drive trip in which 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

Inspect for the following conditions:

    • A mis-routed harness. Inspect the MAF sensor harness for routing that is too close to the following components:
       - Secondary ignition wires or coils
       - Solenoids
       - Relays
       - Motors
    • The throttle plate for sticking, or for deposits on the throttle plate, or in the throttle bore.
    • Any un-metered air that enters the engine may cause this DTC to set. Make sure that the oil dip stick is seated, and the oil fill-cap is secure.

For an intermittent condition, refer to Intermittent Conditions .

Test Description

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

  1. This step verifies that the MAP sensor voltage is not too low. The Alternative Fuels ECM uses the MAP sensor value in order to calculate the predicted MAF sensor flow.

  2. This step verifies that the MAP sensor voltage is not too high. The Alternative Fuels ECM uses the MAP sensor value in order to calculate the predicted MAF sensor flow.

  3. This step compares the MAP sensor kPa value to a known good vehicle.

    4.

  4. The step tests the MAP sensors ability to respond to a change in the engine vacuum when the engine is started.

    5.

  5. This step verifies that the TP sensor is not the cause of this DTC. The Alternative Fuels ECM uses the TP sensor value in order to calculate the predicted MAF sensor flow.

  6. Any un-metered air entering the engine may cause this DTC to set. This step eliminates any conditions which can cause a DTC to set with a normally operating MAF sensor.

    7.

  7. A high resistance in the ignition voltage circuit of the MAF sensor may cause this DTC to set.

Step

Action

Values

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. Start the engine.
  2. Observe the Diagnostic Trouble Code (DTC) Information from the following control modules with a scan tool:
    3. • Alternative Fuels ECM
    • PCM

Does the scan tool display any other DTCs?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3
  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 4

Go to Diagnostic Aids

4

  1. Idle the engine.
  2. Observe the MAP sensor voltage parameter with a scan tool.

Does the scan tool indicate that the MAP sensor voltage is less than the specified value?

0.8 V

Go to DTC P0107

Go to Step 5

5

Does the scan tool indicate that the MAP sensor voltage is more than the specified value?

4.0 V

Go to DTC P0108

Go to Step 6

6

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the MAP sensor kPa parameter with a scan tool.
  3. Compare the MAP sensor kPa parameter to a known good vehicle.

Is the MAP sensor kPa parameter within the specified value of the known good vehicle?

3.0 kPa

Go to Step 7

Go to DTC P0106

7

  1. Observe the MAP sensor voltage parameter with a scan tool.
  2. Start the engine.

Does the MAP sensor voltage parameter change value after you started the engine?

--

Go to Step 8

Go to DTC P0106

8

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the TP sensor voltage parameter with a scan tool.
  3. Press the accelerator pedal from a closed throttle position, to a wide open throttle position.

Does the TP sensor voltage parameter go from below the specified value to above the specified value?

Below 1.0 V to above 4.0 V

Go to Step 9

Go to DTC P0121

9

  1. Inspect for the following conditions:
    2. • MAF sensor wiring harness improperly routed
    • An intake air duct leak
    • A collapsed or damaged intake air duct
    • An intake manifold or throttle body vacuum leak
    • Debris near the MAF sensor inlet screen or damage to the inlet screen
    • An improperly installed MAF sensor. Inspect the flow arrow for proper sensor installation
    • A positive crankcase ventilation (PCV) system leak
    • An incorrect PCV valve, or faulty operation
    • A loose or missing oil fill cap
  2. Repair any condition as necessary.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 10

10

  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the MAF sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the ignition voltage circuit of the MAF sensor and a good ground. Refer to Circuit Testing in Wiring Systems in the C/K Pickup Service Manual.
  5. Connect a DMM to the probe of the test lamp and a good ground.

Does the voltage measure near the specified value?

B+

Go to Step 11

Go to Step 12

11

Test for an intermittent and for a poor connection at the MAF sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

12

Repair the high resistance in the ignition voltage circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you complete the repair?

--

Go to Step 14

--

13

Replace the MAF 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 14

--

14
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC run and pass?

--

Go to Step  15

Go to Step 2

15

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