Circuit Description
The mass air flow (MAF) sensor measures the amount of air ingested by the engine. The direct measurement of the air entering the engine is more accurate than calculating the airflow from the manifold absolute pressure (MAP), the intake air temperature (IAT), and the engine speed. The MAF sensor has an ignition positive voltage, a ground, and a signal circuit. The IAT sensor is also part of the MAF sensor.
The MAF sensor used on this engine is a hot wire type. This engine uses the MAF sensor in order to measure air flow rate. The MAF output frequency is a function of the power required to keep the air flow sensing elements such as hot wires at a fixed temperature above the ambient temperature. Air flowing through the sensor cools the sensing elements. The amount of cooling is proportional to the amount of air flow. The MAF sensor requires a greater amount of current in order to maintain the hot wires at a constant temperature as the air flow increases. The MAF sensor converts the changes in current draw to a frequency signal read by the powertrain control module (PCM). The PCM calculates the air flow in grams per second or hertz, based on this signal.
The PCM monitors the MAF sensor frequency. The PCM determines if the sensor is stuck low, stuck high, not providing the airflow value expected for a given operating condition, or that the signal appears to be stuck based on a lack of signal variation expected during the normal operation. This diagnostic checks for too low an airflow rate. This diagnostic trouble code (DTC) sets when the PCM detects that the MAF sensor frequency is below a predetermined value.
Conditions for Running the DTC
| • | The engine speed is more than 300 RPM. |
| • | The system voltage is more than 8 volts. |
| • | Engine operating more than 1 second. |
Conditions for Setting the DTC
| • | The MAF frequency is less than 10 Hz. |
| • | All conditions are met for 1 second. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
| • | The PCM utilizes speed density such as RPM, MAP, and IAT for fuel management. |
| • | The transmission line pressure increases. |
| • | Firmer transmission shifts |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
The following may cause an intermittent:
| • | Mis-routed harness |
| • | Rubbed through wire insulation |
| • | Broken wire inside the insulation |
For an intermittent, refer to Symptoms .
Any unmetered air may cause this DTC to set. Check for the following:
| • | An engine vacuum leak |
| • | The postive crankcase ventilation (PCV) system for vacuum leaks |
| • | An incorrect PCV valve |
| • | The engine oil dip stick not fully seated |
| • | The engine oil fill cap loose or missing |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Monitoring the MAF sensor frequency determines if the fault is present or the malfunction is intermittent.
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Using the Freeze Frame and Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and 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 or a fail. Operate the vehicle within the same Freeze Frame conditions such as RPM, load, vehicle speed, temperature, etc. that you observed. This will isolate when the DTC failed.
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This step tests whether the MAF sensor ignition positive voltage circuit is shorted to a ground. If the fuse is open, repair the circuit as necessary and replace the fuse.
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This step tests whether 5.0 volts is available to the MAF sensor signal circuit.
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This step tests if the signal circuit is shorted to another 5.0 volt reference circuit. If another DTC sets, repair the circuits that are shorted together. If no DTCs set, it may be necessary to road test the vehicle.
-
This step tests whether B+ is available at the MAF sensor.
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 ENG I fuse open? | -- | |||
Is the voltage near the specified value? | 5 V | |||
Do any additional DTCs set? | -- | |||
7 |
Does the DMM display any voltage? | -- | ||
8 |
Does the DMM display OL? | -- | ||
9 | Test for continuity from the MAF sensor signal circuit to the battery ground using the DMM. Does the DMM display OL? | -- | ||
10 | Test for continuity at the PCM harness between the MAF sensor signal circuit and all other circuits at both PCM connectors using the DMM. Does the DMM indicate continuity between any other circuit? | -- | ||
Connect the J 35616-200 test lamp between the MAF sensor ignition positive voltage circuit and the ground circuit at the MAF sensor harness connector. Is the test lamp illuminated? | -- | |||
12 | Connect the J 35616-200 test lamp between the MAF sensor ignition positive voltage circuit and the battery ground. Is the test lamp illuminated? | -- | ||
13 |
Did you find a poor connection? | -- | ||
14 | Locate and repair the short to voltage in the MAF sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
15 | Locate and repair the open in the MAF sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
16 | Locate and repair the short to ground in the MAF sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
17 | Repair the circuits that are shorted together. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
18 | Repair the MAF sensor ground circuit for an open. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
19 |
Is the action complete? | -- | -- | |
20 | Repair the circuits that are shorted together between the MAF sensor signal circuit and the circuit for which the DTC set. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
21 | Replace the MAF sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Is the action complete? | -- | -- | |
22 |
Did you find and correct the condition? | -- | ||
23 |
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
24 |
Does the scan tool indicate that this test ran and passed? | -- | ||
25 | 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 |
