BI-Fuel/Alternative Fuels

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).

This DTC is used to indicate a MAF sensor frequency that 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 using a scan tool.
^ Interruption of Control Module (AF ECM I VCM I PCM or ECM) power or ground MAY clear DTC Information. Clearing DTC Information with this method is in-consistent and should not be performed.

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 - Computers and Control Systems. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in Diagnostic System Check - Alternative Fuels (Computers and Control Systems). Initial Inspection and Diagnostic Overview Intermittent Conditions

TEST DESCRIPTION

Steps 1-10:

Steps 11-17:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the failure condition affects the gasoline Control module.
3. This step determines if the failure condition is present.
5. This step determines if the proper MAF Signal circuit voltage is available from the gasoline Control module.
9. This step tests for proper MAF sensor ignition voltage and ground circuits.
10. This step determines if the MAF sensor ignition voltage circuit or the MAF sensor ground circuit is the cause of the condition.