For 1990-2009 cars

### Circuit Description

The mass air flow (MAF) sensor is an air flow 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 deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load situation. The MAF sensor has an ignition 1 voltage circuit, a ground circuit and 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 PCM uses the barometric pressure, air density, manifold pressure, throttle position, and the engine RPM in order to calculate a predicted MAF value. The PCM compares the actual MAF sensor signal to the predicted MAF value in order to 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 will set if the actual MAF sensor signal is not within a predetermined range of the calculated MAF value.

### Conditions for Running the DTC

• | DTCs P0102, P0103, P0107, P0108, P0121, P0122, P0123, P0401, P0404, P0405, P0440, P0442, P0446, P1404, or P1441 are not set.

• | The engine is running.

• | The ignition 1 signal is at least 9 volts and is no more than 18 volts.

• | The throttle position (TP) sensor angle is no more than 25 percent.

• | The TP sensor is steady for greater than 1.5 seconds.

• | The manifold absolute pressure (MAP) sensor is no more than 63 kPa.

• | The MAP sensor is steady for greater than 3 seconds.

### Conditions for Setting the DTC

The actual MAF sensor signal is not within a predetermined range of the calculated MAF value.

### 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:

• | A misrouted harness--Inspect the harness of the MAF sensor in order to ensure that the harness is not routed too close to the following components:

• | The secondary ignition wires or coils

• | Any solenoids

• | Any relays

• | Any motors

• | The throttle plate sticking or excessive deposits on the throttle plate or in the throttle bore

• | Any unmetered air entering the engine may cause this DTC to set. Ensure that the oil dipstick is fully seated and the oil fill cap is secure.

• | A wide-open throttle (WOT) acceleration from a stop should cause the MAF sensor value displayed on a scan tool to increase from about 4-7 g/s at idle to 100 g/s or more at the time of the 1-2 shift. If not, inspect for a restriction.

• | The barometric pressure that is used in order to calculate the predicted mass air flow value is based on the MAP sensor reading at key ON. A skewed MAP sensor will cause the calculated mass air flow 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 displayed at or near sea level. The value decreases by approximately 3 kPa for every 1,000 feet of altitude.

• | Inspect for an unresponsive MAP sensor due to the following:

• | Poor vacuum connections

• | A damaged vacuum source

• | Any damaged vacuum hoses

• | Any unmetered air into the manifold

If you suspect the vehicle condition may be related to aftermarket accessories, refer to Checking Aftermarket Accessories in Wiring Systems.

If the problem is intermittent, refer to Intermittent Conditions .

### Test Description

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

1. Diagnose any MAF, MAP, TP, or system voltage DTCs before using this table. If a misfire condition exists or a rough running condition is observed with or without DTC P0300, proceed to DTC P0300 first.

2. Any unmetered air entering the engine may cause this DTC to set. This step eliminates any conditions which can cause a DTC to set with a normally operating MAF sensor.

3. This step verifies the signal circuit from the MAF sensor electrical connector to the PCM. A voltage reading of less than 4 volts or greater than 6 volts indicates a malfunction in the wiring or a poor connection.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls ? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Install a scan tool.
2. Start the engine.
3. Monitor the diagnostic trouble code (DTC) Information using the scan tool.

Does the scan tool display any other DTCs set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3 |

1. Observe and record the Freeze Frame/Failure Records data for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Let the engine idle at the normal operating temperature.
2. With a scan tool observe the MAP sensor voltage parameter.

Does the scan tool indicate that the MAP sensor voltage is within the specified range?

0.8-4 V

Go to Step 5

Go to Manifold Absolute Pressure Sensor Diagnosis

5 |

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

• | Objects blocking the air inlet screen of the MAF sensor

• | A plugged or collapsed intake air duct or dirty air filter element

3. Inspect for vacuum leaks in the following components:

• | The intake manifold

• | The throttle body

• | The exhaust gas recirculation (EGR) valve flange and pipe

• | The MAF sensor seal

• | The MAP sensor seal

• | The evaporative emission (EVAP) canister purge valve seal

• | The fuel meter body seal

• | The crankcase ventilation system

• | The brake booster system

• | The air induction system

Did you find and correct the condition?

--

Go to Step 23

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Remove the MAP sensor from the engine vacuum source. Refer to Manifold Absolute Pressure Sensor Replacement .
3. Leave the electrical harness connected.
4. Connect a hand operated vacuum pump to the MAP sensor.
5. Turn ON the ignition, with the engine OFF.
6. With a scan tool observe or record the MAP sensor kPa parameter display as you SLOWLY apply vacuum 1 inch Hg at a time up to 20 inches Hg as indicated on the pump gauge. Each 1 inch of vacuum applied should result in a 3-4 kPa drop in the MAP sensor value on the scan tool. The value should change smoothly with each 1 inch increase in vacuum.

Does the scan tool indicate that the MAP sensor value changed smoothly through the entire range of the test?

--

Go to Step 7

Go to Manifold Absolute Pressure Sensor Diagnosis

7 | Apply 20 inches Hg vacuum to the MAP sensor. Does the scan tool indicate that the MAP sensor reading is equal to or less than the specified value? | 34 kPa | Go to Step 8 | Go to Manifold Absolute Pressure Sensor Diagnosis
8 | Disconnect the vacuum source from the MAP sensor. Does the scan tool indicate that the MAP sensor reading returned to the original value that was observed in step 6? | -- | Go to Step 9 | Go to Manifold Absolute Pressure Sensor Diagnosis
9 | With a scan tool, observe the TP sensor angle parameter from closed throttle to wide-open throttle. Does the scan tool indicate that the TP sensor value changed smoothly and completely through the specified range of the test? | 0-100% | Go to Step 10 | Go to DTC P0121
10 |

1. Turn OFF the ignition.
2. Disconnect the harness connector of the MAF sensor. Refer to Mass Airflow Sensor Replacement .
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage from the signal circuit of the MAF sensor to a good ground. Refer to Circuit Testing in Wiring Systems.

Does the voltage measure near the specified value?

5.0 V

Go to Step 11

Go to Step 12

11 | Connect a test lamp between the ignition 1 voltage circuit of the MAF sensor and the ground circuit of the MAF sensor. Refer to Circuit Testing in Wiring Systems. Does the test lamp illuminate? | -- | Go to Step 19 | Go to Step 14
12 | Does the voltage measure less than the specified value? | 4.5 V | Go to Step 15 | Go to Step 13
13 | Important:: Disconnecting the PCM connectors may eliminate the short to voltage if the signal circuit is shorted to another PCM circuit. Refer to Circuit Testing in Wiring Systems.

1. Turn OFF the ignition.
2. Disconnect the PCM. Refer to Powertrain Control Module Replacement .
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage from the signal circuit of the MAF sensor to a good ground.

Does the voltage measure near the specified value?

0.0 V

Go to Step 22

Go to Step 18

14 | Connect a test lamp between the ignition 1 voltage circuit of the MAF sensor and a good ground. Refer to Circuit Testing in Wiring Systems. Does the test lamp illuminate? | -- | Go to Step 16 | Go to Step 17
15 |

1. Turn OFF the ignition.
2. Disconnect the PCM. Refer to Powertrain Control Module Replacement .
3. Test the signal circuit between the PCM and the MAF sensor for the following conditions:

• | A high resistance or an open

• | A short to ground

• | A short to the ground circuit of the MAF sensor--Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 20

16 | Repair the high resistance or an open in the ground circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 23 | --
17 |

1. Repair the short to ground or an open in the ignition 1 voltage circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems.
2. Replace the fuse if necessary.

Did you complete the repair?

--

Go to Step 23

Go to Step 21

18 | Repair the short to voltage in the signal circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 23 | --
19 | Inspect for poor connections at the harness connector of 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 23 | Go to Step 21
20 | Inspect for poor connections at the harness connector of the PCM. 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 23 | Go to Step 22
21 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Did you complete the replacement? | -- | Go to Step 23 | --
22 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 23 | --
23 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 24

Go to Step 2

24 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK