For 1990-2009 cars

### Circuit Description

The intake flow rationality diagnostic provides the within-range rationality check for the mass air flow (MAF), manifold absolute pressure (MAP), and the throttle position (TP) sensors. This is an explicit model-based diagnostic containing 4 separate models for the intake system.

• | The throttle model describes the flow through the throttle body and is used to estimate the MAF through the throttle body as a function of barometric pressure (BARO), TP, intake air temperature (IAT), and estimated MAP.

• | The first intake manifold model describes the intake manifold and is used to estimate MAP as a function of the MAF into the manifold from the throttle body and the MAF out of the manifold caused by engine pumping. The flow into the manifold from the throttle uses the MAF estimate calculated from the above throttle model.

• | The second intake manifold model is identical to the first intake manifold model except that the MAF sensor measurement is used instead of the throttle model estimate for the throttle air input.

• | A fourth model is created from the combination and additional calculations of the throttle model and the first intake manifold model.

The estimates of MAF and MAP obtained from this system of models and calculations are then compared to the actual measured values from the MAF, MAP, and the TP sensors and to each other to determine the appropriate DTC to fail. The following table illustrates the possible failure combinations and the resulting DTC or DTCs.

Throttle Model | First Intake Manifold Model | Second Intake Manifold Model | Fourth Model | DTCs Passed | DTCs Failed
X | X | Pass | Pass | P0101 P0106 P0121 P1101 | None
Pass | Pass | Failed | Pass | P0101 P0106 P0121 P1101 | None
Failed | Pass | Failed | Pass | P0106 P0121 P1101 | P0101
Pass | Failed | Failed | Pass | P0101 P0121 P1101 | P0106
Failed | Failed | Failed | Pass | P0121 P1101 | P0101 P0106
X | X | Pass | Failed | P0101 P0106 P1101 | P0121
Pass | Pass | Failed | Failed | P0101 P0106 P0121 P1101 | None
Failed | Pass | Failed | Failed | P0101 P0106 P0121 | P1101
X | Failed | Failed | Failed | P0101 P0106 P0121 | P1101

If the powertrain control module (PCM) detects that the actual measured airflow from MAF, MAP, and TP is not within range of the calculated airflow that is derived from the system of models DTC P0101 sets.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0101 Mass Air Flow (MAF) System Performance

### Conditions for Running the DTC

• | DTCs P0102, P0103, P0112, P0113, P0107, P0108, P0117, P0118, P0335, P0336 are not set.

• | The engine speed is between 400-6,400 RPM.

• | The IAT Sensor parameter is between -7 and +125°C ( +19 and +257°F).

• | The ECT Sensor parameter is between 70-125°C (158-257°F).

• | This DTC runs continuously within the enabling conditions.

### Conditions for Setting the DTC

The PCM detects that the actual measured airflow from MAF, MAP, and TP is not within range of the calculated airflow that is derived from the system of models for more than 0.5 second.

### 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 the harness of the MAF sensor to verify that it is not routed too close to the following components:

- | Any aftermarket accessories--Refer to Checking Aftermarket Accessories .

- | Any solenoids

- | Any relays

- | Any motors

• | A wide open throttle acceleration from a stop should cause the MAF sensor parameter on the scan tool to increase rapidly. This increase should be from 3-6 g/s at idle to 140 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.

• | A skewed or stuck engine coolant temperature (ECT) or IAT sensor will cause the calculated models to be inaccurate and may cause this DTC to run when it shouldn't.

• | A steady or intermittent high resistance of 15 ohms or more on the ignition 1 voltage circuit will cause the MAF sensor values to be skewed high by up to 60 g/s, and may cause this DTC to set. A high resistance will cause a driveability concern before this DTC sets.

• | The BARO that is used by the PCM to calculate the air flow models is initially based on the MAP sensor at key ON. When the engine is running, the PCM will continually update the BARO value near wide open throttle using the MAP sensor and a calculation. A skewed MAP sensor will cause the calculated mass air flow value to be inaccurate and may result in a no start condition. With the ignition ON and the engine OFF, the MAP Sensor parameter varies with the altitude. 101 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 305 meters (1,000 feet) of altitude.

• | A high resistance on the low reference circuit of the MAP sensor will skew the sensor value and may cause this DTC to set.

• | If the condition is intermittent, refer to Testing for Intermittent Conditions and Poor Connections .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step will determine if any mechanical faults have caused this DTC to set.

2. This voltage drop test will determine if high resistance has caused this DTC to set.

3. This step verifies the voltage signal from the PCM to the MAF sensor connector.

4. This step will determine if the PCM can accurately process the frequency signal that it receives from the MAF sensor.

5. This step will determine if an abnormal resistance of less than 1,150 ohms has skewed the MAF sensor frequency signal.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Important: A stalling condition created by any of the following DTCs may cause this DTC to set. Are DTCs P0641, P0651, P1516, P2101, P2119 or P2135 set? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | Go to Step 3
3 | Important: This diagnostic routine may have to be followed more than once. Attempt to start the engine. Does the engine start? | -- | Go to Step 4 | Go to Step 5
4 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 60 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 5

Go to Diagnostic Aids

5 |

1. Turn OFF the ignition.
2. Inspect for the following conditions:

• | A restricted or collapsed air intake duct

• | A misaligned air intake duct

• | A dirty or deteriorating air filter element

• | Any objects blocking the air inlet probe of the mass air flow (MAF)/intake air temperature (IAT) sensor

• | Any contamination or debris on the sensing elements in the probe of the MAF/IAT sensor

• | Any water intrusion in the induction system

• | Any vacuum leak downstream of the MAF/IAT sensor

• | An intake manifold leak

• | An engine misfire--Review the Freeze Frame/Failure records.

• | A manifold absolute pressure (MAP) sensor seal that is missing or damaged

• | A skewed or stuck engine coolant temperature (ECT) or IAT sensor--Refer to Temperature Versus Resistance .

• | Any type of restriction in the exhaust system--Refer to Restricted Exhaust .

Did you find and correct the condition?

--

Go to Step 24

Go to Step 6

6 | Important:: The Altitude vs. Barometric Pressure table indicates a pressure range for a given altitude under normal weather conditions. Weather conditions consisting of very low or very high pressure and/or temperature may cause a reading to be slightly out of range.

1. Accurately determine the altitude.
2. Turn ON the ignition, with the engine OFF.
3. Observe the MAP Sensor kPa parameter with a scan tool.
4. The MAP sensor pressure should be within the specified range for your altitude. Refer to Altitude Versus Barometric Pressure .

Is the MAP sensor pressure within the specified range as indicated on the Altitude vs. Barometric pressure table?

--

Go to Step 7

Go to DTC P0106

7 |

1. Observe the MAP Sensor kPa parameter with a scan tool.
2. Start the engine.

Does the MAP Sensor kPa parameter decrease?

--

Go to Step 8

Go to DTC P0106

8 |

1. Idle the engine.
2. Take a snapshot of the Engine Data list while performing the following action. Refer to Scan Tool Snapshot Procedure .
3. Depress the accelerator pedal quickly to a wide open throttle, then release it.
4. Exit from the snapshot and review the data.
5. Observe the MAP Sensor kPa parameter through the range of the test.

Does the MAP Sensor parameter change to within 5 kPa of the BARO parameter?

--

Go to Step 9

Go to DTC P0106

9 |

1. Turn OFF the ignition.
2. Turn ON the ignition, with the engine OFF.
3. Observe The TP Indicated Angle parameter with a scan tool.
4. Depress the accelerator pedal completely.

Is the TP Indicated Angle parameter within the specified range?

99-100%

Go to Step 10

Go to DTC P1516

10 | Take a snapshot of the TAC Data list while performing the following action. Refer to Scan Tool Snapshot Procedure .

1. Slowly depress the accelerator pedal to wide-open throttle and then slowly release the pedal.
2. Exit from the snapshot and review the data.
3. Compare the TP Sensor 1 and the TP Sensor 2 parameters frame by frame.

Is the difference between the parameters at any time more than the specified value?

2%

Go to DTC P2135

Go to Step 11

11 | Inspect the throttle body and the throttle valve for the following conditions:

• | Any damage

• | Any restriction that could affect the air flow through the throttle body or the throttle valve

• | Any missing parts

• | A throttle valve that is not fully open when the accelerator pedal is fully depressed

Did you find and correct the condition?

--

Go to Step 24

Go to Step 12

12 |

1. Measure the battery voltage with a DMM.
2. Disconnect the MAF/IAT sensor.
3. Connect a test lamp between the ignition 1 voltage circuit of the MAF sensor and a good ground. Refer to Probing Electrical Connectors .
4. Connect the DMM to the probe of the test lamp and a good ground. Refer to Measuring Voltage Drop and Circuit Testing .

Is the voltage within 1 volt of the specified value?

B+

Go to Step 13

Go to Step 20

13 | Important: All electrical components and accessories must be turned OFF.

1. Turn OFF the ignition for 60 seconds to allow the control modules to power down.
2. Measure the resistance from the ground circuit of the MAF sensor to a good ground with a DMM. Refer to Circuit Testing .

Is the resistance less than the specified value?

5 ohms

Go to Step 14

Go to Step 21

14 |

1. Turn ON the ignition, with the engine OFF.
2. Measure the voltage from the signal circuit of the MAF sensor to a good ground with a DMM. Refer to Circuit Testing .

Is the voltage within the specified range?

4.9-5.2 V

Go to Step 15

Go to Step 17

15 |

1. Turn OFF the ignition.
2. Connect the voltage supply and ground the black lead of the J 38522 Variable Signal Generator to the vehicle.
3. Connect the red lead of the J 38522 to the signal circuit of the MAF sensor. Refer to Probing Electrical Connectors .
4. Set the Duty Cycle switch of the J 38522 to Normal.
5. Set the Frequency switch of the J 38522 to 5 K.
6. Set the Signal switch of the J 38522 to 5 V.
7. Start the engine and allow it to idle.
8. Observe the MAF Sensor parameter with a scan tool.

Is the MAF Sensor parameter within the specified range?

4950-5025 Hz

Go to Step 16

Go to Step 17

16 | Important: The J 38522 is able to overcome an abnormal resistance on the signal circuit of up to 1,150 ohms. The MAF sensor will not be able to overcome a resistance this high.

1. Turn OFF the ignition.
2. Disconnect the powertrain control module (PCM).
3. Test the MAF sensor signal circuit for the following conditions:

• | A high resistance

| Important: The following short will skew the MAF sensor reading by 35 g/s or more at a wide-open throttle acceleration.

• | A short to the IAT signal circuit

• | Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 24

Go to Step 18

17 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Test the MAF sensor signal circuit for the following conditions:

• | A high resistance

• | An intermittent open circuit

• | A high resistance short to ground

• | A short to the IAT signal circuit

• | Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 24

Go to Step 19

18 | Test for an intermittent and for a poor connection at the MAF/IAT sensor. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Repairing Connector Terminals . Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 22
19 | Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Repairing Connector Terminals . Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 23
20 | Repair the high resistance or the intermittent open in the MAF sensor ignition 1 voltage circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 24 | --
21 | Repair the high resistance or the intermittent open in the MAF sensor ground circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 24 | --
22 | Replace the MAF/IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 24 | --
23 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 24 | --
24 | Important: This diagnostic routine may have to be followed more than once.

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 60 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 25

25 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK