Circuit Description
The Mass Air Flow (MAF) sensor measures the amount of air that is ingested by the engine. The direct measurement of air entering the engine is more accurate than calculating the airflow from speed/density (MAP, IAT, and RPM ). The MAF sensor has a battery feed, ground and signal circuit. The MAF sensor used on this vehicle is a hot wire type and is used to measure the air flow rate. The MAF output frequency is a function of the power required to keep the air flow sensing elements (hot wires) at a fixed temperature above ambient temperature. Air flowing through the sensor cools the sensing elements. The amount of cooling is proportional to the amount of air flow. As the air flow increases, a greater amount of current is required to maintain the hot wires at a constant temperature. The MAF sensor converts the changes in current draw to a frequency signal which is read by the PCM. The PCM calculates air flow (gram per seconds) based on this signal. The PCM monitors the MAF sensor frequency and can determine if the sensor is stuck low, high, or not providing the airflow value expected for a given operating condition. Another possibility the signal appears to be stuck based on a lack of signal variation expected during normal operation. This diagnostic checks for too low of an airflow rate. When the PCM detects that the MAF sensor grams per second is below a predetermined value.
Conditions for Setting the DTC
| • | The engine is OFF |
| • | The ignition is ON for 2 seconds |
| • | MAF sensor is no more than 60Hz |
Low Frequency Test
| • | The engine is running. |
| • | Engine run time is greater than 0.4 seconds. |
| • | System voltage isgreater than 8.0 volts. |
| • | Throttle Position is less than 89.8%. |
| • | MAF signal frequency is no more than 2 g/s. |
| • | Above conditions present for greater than 2 seconds |
| • | This DTC sets if the signal from the MAF senor measures below the possible range of a normally operating MAF sensor. |
Action Taken When the DTC Sets
| • | The PCM turns on the malfunction indicator lamp (MIL) after 2 consecutive driving cycles with the fault active. |
| • | The PCM will utilize speed density (RPM, MAP, IAT) for fuel management. |
| • | The PCM will record operating conditions at the time the diagnostic fails. The first time the diagnostic fails, this information will be stored in Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the operating conditions at the time of failure will be written to Freeze Frame and the Failure record will be updated. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle). |
| • | Use the scan tool Clear Information function. |
| • | A last test failed (Current DTC) will clear when the diagnostic runs and does not fail. |
| • | Disconnect the PCM battery feed for 30 seconds. |
Diagnostic Aids
Important: Water entering the air intake system that reaches the MAF sensor could cause this DTC to set. The water rapidly cools the hot wires in the sensor, causing a false indication of excessive airflow. Inspect the air intake system for evidence (witness marks) of water intrusion.
Inspect for a poor connections at the PCM. Perform the following procedures:
| • | Inspect harness connectors for the following conditions: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connection |
| • | Inspect for a misrouted harness. Inspect the MAF sensor harness in order to ensure that it is not routed too close to high voltage wires such as spark plug leads. |
| • | Inspect for a damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving the connectors and the wiring harnesses related to the MAF sensor. A change in the display indicates the location of the fault. |
| • | Inspect for any unmetered air. Unmetered air may cause this DTC to set. Inspect for the following conditions: |
| - | An engine vacuum leak |
| - | The PCV system for vacuum leaks |
| - | An incorrect PCV valve |
| - | The oil dip stick not fully seated |
| - | The engine oil fill cap loose or missing |
For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit prevents any damage to the harness connector terminals.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Monitoring the MAF sensor frequency will determine if the fault is present or the malfunction is intermittent. For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit will prevent any damage to the harness connector terminals.
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Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit prevents any damage to the harness connector terminals.
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This step checks whether the MAF sensor signal circuit is open or shorted to a ground. If 5.0 volts is present the circuit is OK.
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This step checks whether the B+ supply and the ground circuit are OK.
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This step checks whether B+ is available at the MAF sensor.
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Inspect the ENG-1 20 amp fuse for being open. If the fuse is open, inspect the MAF sensor ignition feed circuit for a short to ground. If no voltage is on the ignition feed circuit to the MAF sensor, inspect the ignition relay for proper operation. Probe both sides of the ENG-1 fuse in order to determine if the ignition switch is suppling the voltage. Refer to Body and Accessories for further diagnosis of the ignition switch.
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Inspect for proper terminal tension/connections at the PCM harness before replacing the PCM.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||
Is the MAF sensor frequency below the specified value? | 10 Hz | |||||||||||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | ||||||||||
Is the voltage near the specified value? | 5.0V | |||||||||||
Connect a test lamp J 35616-200 between the MAF sensor ignition feed circuit and the ground circuit at the MAF sensor harness connector. Is the test lamp illuminated? | -- | |||||||||||
Connect a test lamp J 35616-200 between the MAF sensor ignition feed circuit and the battery ground. Is the test lamp illuminated? | -- | |||||||||||
7 |
Did you find a poor connection? | -- | ||||||||||
8 |
Did you find the MAF sensor signal circuit open or shorted? | -- | ||||||||||
9 | Locate and repair the open in the ground circuit to the MAF sensor. Refer to Body and Accessories/Wiring Systems. Is the action complete? | -- | -- | |||||||||
Repair the ignition feed circuit to the MAF sensor. Refer to Body and Accessories/Wiring Systems. Is the action complete? | -- | -- | ||||||||||
11 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Is the action complete? | -- | -- | |||||||||
12 |
Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement . Replace the PCM. Is the action complete? | -- | -- | |||||||||
13 |
Does the scan tool indicate that this test ran and passed? | -- | ||||||||||
14 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
