GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD (LPG) 🢒 Engine 🢒 Engine Controls - 6.0L 🢒 DTC P0102

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.

This DTC sets when the MAF sensor frequency is below the normal operating range of the sensor.

Conditions for Running the DTC

Cranking Test

    • The engine is cranking on alternative fuel, but has not yet started.
    • The battery voltage is more than 8 volts.

Running Test

    • The engine is operating on alternative fuel.
    • The engine has been operating for more than 10 seconds.
    • The battery voltage is more than 10 volts.
    • The engine speed is more than 500 RPM.

Conditions for Setting the DTC

Cranking Test

The Alternative Fuels ECM monitors a MAF sensor signal of less than 125 Hz (0 gms/sec) for at least 0.5 seconds continuously.

Running Test

The Alternative Fuels ECM monitors a MAF sensor signal of less than 1,500 Hz (2.5 gms/sec) for at least 0.5 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.

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 condition affects the powertrain control module (PCM).

    3.

  3. This step determines if the proper MAF Signal circuit voltage is available from the PCM.

    4.

  4. This step tests for proper MAF sensor ignition voltage and ground circuits.

    5.

  5. This step determines if the MAF sensor ignition voltage circuit or the MAF sensor ground circuit is the cause of the condition.

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. Start and idle the engine.
  2. With a scan tool, establish communication with the powertrain control module (PCM).
  3. Observe the MAF sensor data parameter.

Does the MAF sensor data parameter indicate airflow less than the specified value?

2.5 gms/sec

Go to Step 4

Go to Step 7

4

  1. Turn OFF the ignition.
  2. Disconnect the MAF sensor connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the signal circuit of the MAF sensor to a good ground with a DMM.

Is the voltage near the specified value?

5 V

Go to Step 8

Go to Step 5

5
  1. Inspect the MAF sensor signal circuit for an open or high resistance between the sensor connector and the PCM.
  2. Inspect the MAF sensor signal circuit for a short to voltage if the circuit voltage was more than 5.2 volts. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.
  3. Inspect for proper terminal contact at both the PCM connector and the MAP sensor connector. 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 16

Go to Step 6

6
  1. Inspect the MAF sensor signal circuit for a short to engine ground or to the sensor ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.
  2. Disconnect the Alternative Fuels ECM connector containing the MAF sensor signal circuit in order to determine if the ECM is the cause of the short.

Did you find and correct the condition?

 

Go to Step 16

Go to Step 14

7
  1. Inspect the MAF sensor signal circuit for an open or high resistance between the circuit splice and the Alternative Fuels ECM connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.
  2. Inspect for proper terminal contact at the Alternative Fuels ECM connector. 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 16

Go to Step 15

8

Connect a test lamp between the ignition feed circuit terminal and the ground circuit terminal of the MAF sensor connector.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 9

9

Connect the test lamp between the ignition feed circuit terminal of the MAF sensor connector and a known good ground.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 10

10
  1. Repair the cause of no MAF sensor voltage. Possible causes include the following:
    2. • An open ignition fuse
    • An open or shorted to ground ignition feed circuit
    • A shorted to ground component that shares the MAF sensor ignition feed circuit
  2. Repair the wiring or replace any components as necessary.

Did you complete the repair?

--

Go to Step 16

Go to Step 13

11

Repair the open MAF sensor ground circuit. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you complete the repair?

--

Go to Step 16

--

12

Inspect the MAF sensor connector for proper terminal contact. 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 16

--

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 16

--

14

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 16

--

15

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

Did you complete the replacement?

--

Go to Step 17

--

16
  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 17

Go to Step 2

17

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