Powertrain Management (CNG)

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.
2. This step determines if the condition is present.
3. This step determines if the condition affects the powertrain control module (PCM).
4. This step determines if the proper MAF Signal circuit voltage is available from the PCM.
8. This step tests for proper MAF sensor ignition voltage and ground circuits.
9. This step determines if the MAF sensor ignition voltage circuit or the MAF sensor ground circuit is the cause of the condition.