For 1990-2009 cars
Engine Controls Components
Air Injection Pump, Air Injection Pump Relay K12, MAF and ECT Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The mass air flow (MAF) sensor used on this vehicle is a hot film type and is used to measure the air flow rate. The MAF output voltage is a function of the current required to keep the air flow sensing element at a fixed temperature. The air flowing through the sensor cools the sensing element. The amount of cooling is proportional to the amount of the air flow. As the air flow increases, more current is required in order to maintain the hot film at a constant temperature. The MAF sensor converts the changes in current to a voltage signal read by the engine control module (ECM). The ECM calculates the air flow based on this signal.

The MAF sensor uses the following circuits to operate:

• | Switched battery voltage

• | 5 volt reference

• | Reference ground

• | Signal

The switched battery voltage is supplied from the engine controls power relay. The 5 volt reference for the mass air flow sensor is supplied from the same source in the ECM as the 5 volt reference for accelerator pedal position (APP) sensor 1 and the fuel tank pressure (FTP) sensor. The 5 volt reference voltage for each of the sensors is supplied on separate ECM terminals, but the terminals are connected internally to the shared voltage supply. The reference ground circuit is shared with the following components:

• | Camshaft position (CMP) sensor

• | Intake air temperature (IAT) sensor

• | Engine coolant temperature (ECT) sensor

• | Throttle position (TP) sensor 1

• | Throttle position (TP) sensor 2

The ECM monitors the MAF sensor signal voltage and can determine if the sensor signal voltage is too low, too high, not indicating the expected airflow for a given operating condition, or that the signal appears to be stuck based on the lack of normal signal fluctuations expected during engine operation.

### Conditions for Running the DTC

• | The battery voltage is more than 11 volts.

• | One or both of the following DTCs are not set: P1120, or P1220.

• | The engine speed is more than 500 RPM.

### Conditions for Setting the DTC

The MAF signal indicates an airflow outside of a calculated range for a given RPM for at least 0.1 second.

### Action Taken When the DTC Sets

• | The ECM illuminates the malfunction indicator lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.

• | The ECM will calculate the airflow from the other sensor inputs.

### Conditions for Clearing the MIL/DTC

• | The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and passes.

• | A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic.

• | The scan tool clears the MIL/DTC.

### Test Description

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

1. The engine must remain running in order for the MAF display on the scan tool to update.

2. The ECM provides the reference ground for the MAF sensor. A small amount of voltage will appear on this circuit when the ECM is operational. The measured resistance of the circuit will increase when the ECM is operational. This is considered normal.

3. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. Disconnecting the APP connector will determine if the APP sensor is affecting the 5 volt reference circuit for the MAF sensor.

4. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. Disconnecting the fuel tank connector will isolate the FTP sensor and the fuel tank harness from the remainder of the circuit.

5. Disconnecting the ECM C2 connector will prevent the engine controls power relay from operating. When checking for a short to voltage on an ECM circuit, this relay should be energized. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected inside the ECM. A short to voltage on the 5 volt reference circuit of the APP 1 sensor will affect the operation of the MAF sensor.

6. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. A short to ground on the 5 volt reference circuit of the APP 1 sensor will affect the operation of the MAF sensor.

7. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. A short to ground on the 5 volt reference circuit of the FTP sensor will affect the operation of the MAF sensor.

8. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. A short to voltage on the 5 volt reference circuit of the FTP sensor will affect the operation of the MAF sensor.

#### DTC P0100 - Mass Air Flow (MAF) Sensor Circuit

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Start and idle the engine.
2. With a scan tool, observe the MAF data parameter in the engine data list.

Is the mass air flow reading above the specified value?

39 g/s

Go to Step 7

Go to Step 3

3 |

1. Allow the engine to idle until the engine coolant reaches operating temperature.
2. With the engine idling, use the scan tool in order to monitor the MAF display.

Is the mass air flow below the specified value?

1.1 g/s

Go to Step 8

Go to Step 4

4 |

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

• | Objects blocking the MAF sensor inlet screen

• | Intake manifold vacuum leaks

• | Vacuum leaks at the throttle body

• | MAF sensor for the proper installation

• | Air leaks in the intake duct system between the MAF sensor and the throttle body

• | An improperly functioning crankcase ventilation system

• | A loose or missing engine oil fill cap

• | An unseated engine oil dipstick

3. Repair as necessary.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 5

5 |

1. Start the engine and allow it to idle.
2. Move the harness and the related connectors while using the scan tool to monitor the MAF display.

Does the harness movement affect the mass air flow?

--

Go to Step 30

Go to Step 6

6 |

1. Turn ON the ignition with the engine OFF.
2. Review the Freeze Frame data for this DTC and note the parameters.
3. Clear the DTCs.
4. Turn OFF the ignition for 15 seconds.
5. Start the engine.
6. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions that are recorded in the Freeze Frame as possible. Refer to Conditions for Running the DTC.
7. Check for any DTCs.

Is this DTC set?

--

Go to Step 7

Go to Intermittent Conditions

7 |

1. Disconnect the MAF sensor connector.
2. Ensure the engine remains idling.
3. With a scan tool, observe the MAF data parameter in the engine data list.

Does the scan tool indicate the specified air flow?

0.0 g/s

Go to Step 8

Go to Step 20

8 |

1. Turn OFF the ignition.
2. Disconnect the MAF sensor.
3. Turn ON the ignition, with the engine OFF.

Important: DO NOT use the reference ground located in the MAF/IAT connector for this test. ECM damage will result.

4. Probe the B+ supply circuit for the MAF sensor with the test lamp connected to battery ground.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 26

9 | Using a digital multimeter (DMM), measure the voltage between the MAF 5 volt reference circuit and battery ground. Does the voltage measure within the specified value? | 4.8-5.2 volts | Go to Step 10 | Go to Step 15
10 |

1. Turn OFF the ignition.
2. Connect a 3 amp fused jumper wire between the 5 volt reference circuit and the signal circuit of the MAF sensor.
3. Start and idle the engine.
4. With a scan tool, observe the MAF data parameter in the engine data list.

Does the scan tool indicate MAF more than the specified value?

72 g/s

Go to Step 11

Go to Step 14

11 |

Important: Make sure the ECM has shut down prior to measuring the reference ground circuit resistance. This can be verified by the loss of communication on the scan tool.

1. Turn OFF the ignition for 30 seconds.

Important: Do not use a test lamp to test the continuity of the reference ground. Damage to the ECM will result.

2. Measure the resistance from the reference ground circuit of the MAF sensor to battery ground.

Does the resistance measure less than the specified value?

5 ohms

Go to Step 28

Go to Step 12

12 |

1. Disconnect the ECM connector C1.
2. Test the reference ground circuit of the MAF sensor for an open or high resistance.
3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 13

13 | Measure the resistance from the ECM case to battery ground. Is the resistance of the circuit less than the specified value? | 5 ohms | Go to Step 29 | Go to Step 27
14 |

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

• | Open

• | Short to ground

• | High resistance

4. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 29

15 |

1. Turn OFF the ignition.
2. Disconnect the accelerator pedal position (APP) sensor connector.
3. Turn ON the ignition with the engine OFF.
4. Measure the voltage between the 5 volt reference circuit of the MAF sensor and battery ground using a DMM.

Does the voltage measure within the specified value?

4.8-5.2 V

Go to Step 33

Go to Step 16

16 |

1. Turn OFF the ignition.
2. Disconnect the fuel tank wiring harness connector C400.
3. Turn ON the ignition with the engine OFF.
4. Measure the voltage between the 5 volt reference circuit of the MAF sensor and battery ground using a DMM.

Does the voltage measure within the specified value?

4.8-5.2 V

Go to Step 24

Go to Step 17

17 | Is the voltage less than the specified value? | 5 volts | Go to Step 18 | Go to Step 19
18 |

1. Turn OFF the ignition.
2. Disconnect the ECM connector C1.
3. Test the 5 volt reference circuit for the MAF sensor for the following conditions:

• | Short to ground

• | Open

• | High resistance

4. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 22

19 |

1. Turn OFF the ignition.
2. Disconnect the ECM connector C1.
3. Turn ON the ignition.
4. Test the 5 volt reference circuit for the MAF sensor for a short to voltage.
5. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 21

20 |

1. Turn OFF the ignition.
2. Disconnect the ECM connector C1.
3. Turn ON the ignition with the engine OFF.
4. Test the signal circuit for the MAF sensor for a short to voltage or to a 5-volt reference.
5. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 34

21 |

1. Turn OFF the ignition.
2. Disconnect the ECM connector C2.
3. Turn ON the ignition with the engine OFF.
4. Install a fused jumper wire from the control circuit of the engine controls power relay to ground.
5. Test the 5 volt reference circuit of the APP sensor 1 for a short to voltage.
6. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 25

22 | Test the 5 volt reference circuit of the APP sensor 1 for a short to ground. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 35 | Go to Step 23
23 | Test the 5 volt reference circuit of the FTP sensor for a short to ground. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 35 | Go to Step 29
24 |

1. Turn OFF the ignition.
2. Disconnect the fuel tank pressure (FTP) sensor. Refer to Fuel Tank Pressure Sensor Replacement .
3. Test the 5 volt reference circuit for the FTP sensor in the fuel tank harness for the following conditions:

• | Short to ground

• | Short to the reference ground circuit

• | Short to voltage

4. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 32

25 | Test the 5 volt reference circuit of the FTP sensor for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 35 | Go to Step 34
26 | Repair the open or high resistance in the switched B+ circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 35 | --
27 | Repair the open or high resistance in the ECM ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 35 | --
28 |

1. Inspect for a poor connection or poor terminal tension at the MAF sensor harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 31

29 |

1. Inspect for a poor connection or poor terminal tension at the ECM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections .
2. Repair as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 34

30 | Repair the harness or connections as necessary. Refer to Connector Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 35 | --
31 | Replace the MAF sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 35 | --
32 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 35 | --
33 | Replace the APP sensor. Refer to Accelerator Pedal Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 35 | --
34 | Important: Perform the Idle Learn Procedure when replacing the ECM or the throttle body. Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle.

Replace the ECM. Refer to Engine Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 35

--

35 |

1. Using a scan tool, clear the DTCs.
2. Turn OFF the ignition for 15 seconds.
3. Start the engine.
4. Allow the engine to idle until the engine reaches the normal operating temperature.
5. Select DTC and the Specific DTC function.
6. Enter the DTC number that was set.
7. Operate the vehicle within the Conditions for Running this DTC until the scan tool indicates that the diagnostic Ran.

Does the scan tool indicate that the diagnostic Passed?

--

Go to Step 36

Go to Step 2

36 | Were there any additional DTCs noted during the Powertrain OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | System OK