GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Express (CNG) 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 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 gasoline Control Module (VCM/PCM or ECM) and the Alternative Fuels ECM monitor the MAF signal circuit frequency and determine the flow and mass of the air entering the engine.

The gasoline Control Module (VCM/PCM or ECM) and the Alternative Fuels ECM convert the MAF signal circuit frequency into a grams per second value. During low air flow rates, such as at engine idle, the MAF sensor will produce a low frequency signal, around 2,000 Hz or 6 grams per second. During high air flow rates, such as at wide open throttle-road load, the MAF sensor will produce a high frequency signal, around 9,000 Hz or 125 grams per second.

The gasoline Control Module (VCM/PCM or ECM) 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 gasoline Control Module 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 is used to indicate that 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

Intermittent Condition

A fault not present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to the Intermittent Conditions diagnostic information located in Symptoms - Engine Controls. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in Diagnostic System Check - Alternative Fuels (Engine Controls) .

Test Description

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

  1. When a DTC fails, some data parameters are recorded and stored for possible diagnostic aid. The stored Freeze Frame/Failure Records can be saved into a scan tool and be reviewed later if necessary in order to help diagnose an intermittent or difficult to reproduce condition.

    2.

  2. Any stored sensor/circuit DTCs should be diagnosed prior to diagnosing a system type DTC.

    3.

  3. This DTC determines the calculated air flow based upon the MAP sensor values. The MAP sensor must accurately display manifold pressure in order for this DTC to compare the MAF sensor airflow to the calculated air flow correctly.

    A fault not present will be indicated by the MAP Sensor Performance DTC if the MAP sensor is functioning correctly.

    4.

  4. This DTC determines the calculated air flow based upon the TP sensor values. The TP sensor must accurately display throttle angle in order for this DTC to compare the MAF sensor airflow to the calculated air flow correctly.

    A fault not present will be indicated by the TP Sensor Performance DTC if the TP sensor is functioning correctly.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

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

Go to Step 2

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

2

  1. Capture the DTC information from the Alternative Fuels ECM into the scan tool.
  2. Inspect BOTH the Alternative Fuels ECM and the gasoline Control Module (VCM/PCM or ECM) for other stored sensor DTCs.

Is a sensor DTC stored?

Go to Step 3

Go to Step 4

3

Perform the other sensor DTC diagnosis before attempting diagnosis of this DTC.

Is the other DTC diagnosis and/or repair complete?

Go to Step 10

--

4
  1. Perform a visual/physical inspection for the following conditions:
    2. • Any intake air duct leaks
    • Any collapsed or damaged intake air ducts
    • Any intake manifold and throttle body vacuum leaks
    • An improperly installed or leaking fuel mixer
    • Any 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
    • Any positive crankcase ventilation (PCV) system leaks, such as a loose or missing oil fill cap, an in-correct PCV valve, or faulty operation
  2. Repair any condition as necessary.

Was a repair made?

Go to Step 10

Go to Step 5

5

Perform the MAP Sensor Performance DTC diagnosis and return to this step. Refer to DTC P0106 .

Was a MAP sensor fault present and repaired?

Go to Step 10

Go to Step 6

6

Perform the TP Sensor Performance DTC diagnosis and return to this step. Refer to DTC P0121 .

Was a TP sensor fault present and repaired?

Go to Step 10

Go to Step 7

7
  1. Using the scan tool, clear the DTCs.
  2. Start the engine.
  3. View the captured data Freeze Frame Records for this DTC that was stored in step 2.

    4. Observe the data parameters that give an indication of how the vehicle was being operated when this DTC set.

  4. Select DTC and the Specific DTC function.
  5. Enter the DTC number that was set.
  6. Operate the vehicle, within the Conditions for Setting the DTC and the parameters observed when the DTC set, until the scan tool indicates the diagnostic ran.

Does the scan tool indicate the diagnostic passed?

Go to Step 8

Go to Step 9

8

The fault is not present. Refer to Diagnostic Aids.

Are any DTCs stored that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

Go to Intermittent Conditions

9

Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement in the Engine Controls G Van Service Manual?

Go to Step 10

--

10
  1. Using the scan tool, clear the DTCs.
  2. Start the engine.
  3. View the captured data Freeze Frame Records for this DTC that was stored in step 2.

    4. Observe the data parameters that give an indication of how the vehicle was being operated when this DTC set.

  4. Select DTC and the Specific DTC function.
  5. Enter the DTC number that was set.
  6. Operate the vehicle, within the Conditions for Setting the DTC and the parameters observed when the DTC set, until the scan tool indicates the diagnostic ran.

Does the scan tool indicate the diagnostic passed?

System OK

Go to Step 2