For 1990-2009 cars

### Circuit Description

The DTC P0100 Mass Air Flow (MAF) Sensor Circuit diagnostic detects an out of range sensor signal. The MAF sensor measures the changes in the intake air volume that result from the changes in throttle opening and air density. Air flow measurements are used by the powertrain control module (PCM) in order to determine engine fueling requirements.

The MAF sensor is a hot wire design. A platinum hot wire and a thermister are located in the intake air bypass passage of the MAF sensor housing. The temperature of the platinum hot wire is affected by exposure to air flow and by exposure to air temperature. The platinum hot wire is maintained at a set temperature by controlling the current flow through the wire. The MAF sensor converts the changes in current flow to a voltage signal. The voltage signal from the MAF sensor enables the PCM to detect changes in air density and changes in air volume.

### Conditions for Running the DTC

The ignition is ON or the engine is running.

### Conditions for Setting the DTC

• | An open or a short is detected in the MAF sensor signal circuit when the engine speed is less than 3,000 RPM.

• | The condition is present for at least 3 seconds.

OR:

• | An open or a short is detected in the MAF sensor signal circuit when the engine speed is at least 3,000 RPM.

• | The condition is present for at least 3 seconds.

• | The condition is present on 2 consecutive ignition cycles.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM records the operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

• | The PCM enters the Fail-Safe Function and operates with the ignition timing fixed at 5 degrees before top dead center (BTDC).

### Conditions for Clearing the MIL/DTC

• | The MIL turns OFF after 3 consecutively passing cycles without a fault present.

• | A History DTC will clear after 40 consecutive warm-up cycles without a fault.

• | Perform the scan tool clear DTC Information Function in order to clear the DTC.

### Test Description

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

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step checks for a high input signal from the mass air flow (MAF) sensor.

3. This step checks for a low input signal from the MAF sensor.

4. The MAF sensor has 5 test terminals that are easily reached when the MAF sensor is not attached to the air cleaner housing. The test terminals enable the technician to measure the circuit voltages of the MAF sensor with all components connected.

5. This step is looking for MAF sensor output on the MAF signal high circuit. Air movement around the sensor's hot wire element can cause some fluctuation in the voltage being measured.

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 | Select the MAF sensor parameter on the scan tool. Is the MAF sensor value more than or equal to the specified value? | 185.0 g/s | Go to Step 7 | Go to Step 3
3 | Observe the MAF sensor parameter on the scan tool. Is the MAF sensor less than or equal to the specified value? | 0.39 g/s | Go to Step 5 | Go to Step 4
4 |

1. Clear the DTC Information with the scan tool.
2. Operate the vehicle within the Freeze Frame conditions as specified.

Does a DTC P0100 set?

--

Go to Step 2

Go to Intermittent Conditions

5 |

1. Turn OFF the ignition.
2. Remove the MAF sensor from the air cleaner housing. Refer to Mass Airflow Sensor Replacement .
3. Connect the MAF sensor electrical connector.
4. Turn ON the ignition, with the engine OFF.
5. Probe the test terminal of the ignition positive voltage circuit with a test lamp connected to ground.

Is the test lamp illuminated?

--

Go to Step 6

Go to Step 10

6 |

1. Turn ON the ignition, with the engine OFF.
2. Connect a DMM to the test terminal of the MAF signal high circuit and ground.

Is the MAF signal high circuit voltage within the specified range?

0.5-3.0 V

Go to Step 11

Go to Step 12

7 |

1. Turn OFF the ignition.
2. Disconnect the MAF sensor electrical connector.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp from B+ to the MAF signal low circuit.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 9

8 | Measure the voltage of the MAF signal high circuit on the harness side with a DMM connected to ground. Is the MAF signal high circuit voltage more than the specified value? | 0.5 V | Go to Step 15 | Go to Step 16
9 |

1. Inspect for an open in the MAF sensor signal low circuit.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 17

10 | Repair the open in the MAF sensor ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 18 | --
11 |

1. Inspect for an open in the MAF sensor signal high circuit.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 17

12 | Inspect the MAF signal high circuit for a short to ground. Is the MAF signal high circuit shorted to ground? | -- | Go to Step 14 | Go to Step 13
13 |

1. Turn OFF the ignition.
2. Disconnect the connector C1 of the PCM.
3. Turn ON the ignition, with the engine OFF.
4. Probe the MAF signal high circuit on the harness side with a DMM connected to ground.

Is the voltage more than the specified value?

10 V

Go to Step 17

Go to Step 16

14 |

1. Inspect the MAF signal high circuit for a short to ground between the MAF sensor and the PCM.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 17

15 |

1. Inspect the MAF signal high circuit for a short to voltage.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 17

16 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Is the action complete? | -- | Go to Step 18 | --
17 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 18 | --
18 |

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 19

Go to Step 2

19 | 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