Powertrain Management (CNG)
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 Symptom Related Diagnostic Procedures
Test Description
The numbers below refer to the step numbers on the diagnostic table.
4. 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.
5. 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.
6. This step compares the MAP sensor kPa value to a known good vehicle.
7. The step tests the MAP sensors ability to respond to a change in the engine vacuum when the engine is started.
8. 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.
9. 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.
10. A high resistance in the ignition voltage circuit of the MAF sensor may cause this DTC to set.
