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 and the AF ECU monitor the MAF signal circuit frequency and determine the flow and mass of the air entering the engine.
The gasoline Control Module and the AF ECU 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 2000 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 9000 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. |
| • | Battery voltage is greater than 8 volts. |
Running Test
| • | The engine is operating on alternative fuel. |
| • | The engine has been operating for greater than 10 seconds. |
| • | Battery voltage is greater than 10 volts. |
| • | Engine speed is greater than 500 RPM. |
Conditions for Setting the DTC
Cranking Test
The AF ECU monitors a MAF sensor signal of less than 125 Hz (0 gms/sec) for at least 0.5 seconds continuously.
Running Test
The AF ECU monitors a MAF sensor signal of less than 1500 Hz (2.5 gms/sec) for at least 0.5 seconds continuously.
Action Taken When the DTC Sets
The AF ECU will switch-over to gasoline fuel operation. The AF ECU will not attempt alternative fuel operation until the next ignition key cycle.
| • | The AF ECU will illuminate the MIL and store the DTC as History during ONE drive trip in which the diagnostic runs and fails. |
| • | The AF ECU 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 AF ECU 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 ECU / VCM / PCM or ECM) power or ground MAY clear DTC Information. Clearing DTC Information with this method is inconsistent and should not be performed. |
Diagnostic Aids
Fault Not Present
Fault Not Present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to Intermittent Conditions Symptom diagnosis for additional information. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in the OBD System Check.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
-
This step determines if the failure condition affects the gasoline control module.
-
This step determines if the failure condition is present.
-
This step determines if the proper MAF Signal circuit voltage is available from the gasoline control module.
-
This step tests for proper MAF sensor ignition voltage and ground circuits.
-
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 | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the AF Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Alternative Fuels (AF) Powertrain On Board (OBD) System Check | |||||||||
Does the MAF Sensor data parameter indicate airflow less than the specified value? | 2.2 gms/sec | |||||||||||
Does the MAF Sensor data parameter indicate airflow less than the specified value? | 2.2 gms/sec | |||||||||||
4 | The fault is not present. Refer to Diagnostic Aids. Are any DTC's stored that have not been diagnosed? | -- | Go to the Diagnostic Trouble Code (DTC) List | Go to Intermittent Conditions | ||||||||
Is the voltage near the specified value? | 5.0 volts | |||||||||||
6 |
Was a wiring or terminal repair necessary? | -- | ||||||||||
7 |
Was a repair or replacement necessary? | -- | ||||||||||
8 |
Was a wiring or terminal repair necessary? | -- | ||||||||||
Connect the J 34142-B test lamp between the Ignition Feed circuit terminal and the Ground circuit terminal of the MAF sensor connector. Is the test lamp illuminated? | -- | |||||||||||
Connect the J 35616-200 Un-powered Test Lamp between the Ignition Feed circuit terminal of the MAF sensor connector and a known good ground. Is the test lamp illuminated? | -- | |||||||||||
11 | Repair the cause of no MAF sensor voltage. Possible causes include the following:
Is the repair complete? | -- | -- | |||||||||
12 | Repair the open MAF sensor Ground circuit. Is the repair complete? | -- | -- | |||||||||
13 |
Was a connector terminal repair made? | -- | ||||||||||
14 | Replace the MAF Sensor. Refer to Mass Airflow Sensor Replacement in the Engine Controls section of the gasoline service manual. Is the replacement complete? | -- | -- | |||||||||
15 |
Important: The following control module replacement procedures must all be completed before attempting to operate the vehicle.
Important: In order to perform the variation learn procedure a switch-over to gasoline operation is necessary. Remove the CNG 20 amp fuse in order to perform the switch-over. All of the above procedures are located in the gasoline service manual. Is the replacement complete? | -- | -- | |||||||||
16 |
Is the replacement complete? | -- | -- | |||||||||
17 |
Did this DTC RUN and PASS? | -- | System OK |
