Circuit Description
The mass airflow (MAF) sensor is an airflow meter that measures the amount of air entering the engine. The powertrain control module (PCM) uses the MAF sensor signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has:
| • | An ignition 1 voltage circuit |
| • | A ground circuit |
| • | A signal circuit |
The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage in order to produce a frequency based on inlet air flow through the sensor bore. The frequency varies within a range of around 2,000 hertz at idle to about 10,000 hertz at maximum engine load. The PCM uses the following sensor inputs in order to calculate a predicted MAF value:
| • | The manifold absolute pressure (MAP) |
| • | The throttle position (TP) |
| • | The engine speed (RPM) |
The PCM compares the actual MAF sensor frequency signal to the predicted MAF value. This comparison will determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. DTC P0101 sets if the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value.
Conditions for Running the DTC
| • | The engine speed is more than 250 RPM. |
| • | The ignition 1 signal is between 9-18 volts. |
| • | The change in the manifold absolute pressure (MAP) sensor is less than 3 kPa. |
| • | The TP sensor angle is less than 50 percent. |
| • | The change in the throttle position (TP) sensor angle is less than 1.5 percent. |
| • | The evaporative emission (EVAP) purge solenoid command is less than 100 percent. |
| • | The exhaust gas recirculation (EGR) position sensor is less than 50 percent. |
| • | The above conditions are met for more than 5 seconds. |
Conditions for Setting the DTC
The PCM detects that the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value for more than 5 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
Inspect for the following conditions:
| • | An incorrectly routed harness. Inspect the harness of the MAF sensor in order to verify that the harness is not routed too close to the following components: |
| - | The ignition cassette |
| - | Any solenoids |
| - | Any relays |
| - | Any motors |
| • | A skewed or stuck TP sensor. |
| • | Any excessive deposits on the throttle plate or in the throttle bore. |
| • | A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Inspect for any vacuum leaks downstream of the MAF sensor. |
| • | A wide open throttle (WOT) acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 4-7 g/s at idle to 150 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system. |
| • | The barometric pressure (BARO) that is used in order to calculate the predicted MAF value is initially based on the MAP sensor at key ON. When the engine is running, the manifold air pressure (MAP) sensor value is continually updated near WOT. A skewed MAP sensor will cause the calculated MAF value to be inaccurate. The value shown for the MAP sensor display varies with the altitude. With the ignition ON and the engine OFF, 103 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 305 meters (1,000 ft) of altitude. |
| • | High resistance on the ground circuit of the MAP sensor can cause this DTC to set. |
| • | Any loss of vacuum to the MAP sensor can cause this DTC to set. |
If you suspect the condition may be related to aftermarket accessories, refer to Checking Aftermarket Accessories in Wiring Systems.
If the condition is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step will determine if the MAP sensor voltage is within the proper range at idle.
-
This step will determine if the MAP sensor responds properly to the change in manifold pressure.
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This step will determine if the TP sensor is operating properly.
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This step will determine if any mechanical faults have caused this DTC to set.
Step | Action | Values | Yes | No | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||||||||||
2 |
Does the scan tool display any other DTCs set? | -- | Go to Step 3 | |||||||||||||||||||||
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||||||||||||
Is the MAP sensor voltage within the specified range? | 0.8-4 V | Go to Step 5 | ||||||||||||||||||||||
Does the MAP sensor kPa change smoothly and gradually through the specified range of the test? | -- | Go to Step 6 | ||||||||||||||||||||||
Does the scan tool indicate that the TP sensor angle changed smoothly and completely through the specified range of the test? | 0-100% | Go to Step 7 | Go to DTC P0121 | |||||||||||||||||||||
Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 | |||||||||||||||||||||
8 | Test for an intermittent and for a poor connection at the MAF sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 | ||||||||||||||||||||
9 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||||||||||||||||
10 |
Does the DTC run and pass? | -- | Go to Step 11 | Go to Step 2 | ||||||||||||||||||||
11 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||||||||
