For 1990-2009 cars

### Circuit Description

The DTC P0102 Mass Air Flow (MAF) Sensor Circuit Low Voltage diagnostic monitors the mass air flow sensor signal. The MAF sensor measures the amount of air passing through the sensor and into the intake manifold. The powertrain control module (PCM) uses this information to determine the operating requirements of the engine in order to control fuel delivery. The PCM calculates the engine's fuel requirements by monitoring the current flow on the signal wire from the MAF sensor. When the volume of air entering the MAF sensor increases, the current flow seen by the PCM from the MAF sensor also increases. When the air flow decreases, the current seen by the PCM also decreases. The MAF sensor is located between the air intake tube and the air cleaner in the LH front area of the engine compartment.

### Conditions for Running the DTC

The ignition key is ON or the engine is running.

### Conditions for Setting the DTC

• | MAF sensor output current is less than 0.64 mA.

• | Condition is present for longer than 5 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL).

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

• | The PCM enters the Fail-Safe Function and determines injector drive time according to TP sensor and engine speed.

• | PCM changes idle air control (IAC) valve duty cycle.

• | PCM changes fuel injectors frequency.

### Conditions for Clearing the MIL/DTC

• | The MIL turns OFF after three consecutively passing trips without a fault present.

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

• | Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC.

### Diagnostic Aids

Check for any of the following conditions:

• | A misrouted wiring harness -- Inspect the MAF sensor harness to ensure that it is not routed too close to high voltage wires such as spark plug leads.

• | A damaged wiring harness -- Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving the connectors and the wiring harnesses related to the MAF sensor. A change in the display will indicate the location of the fault.

• | Check for an air intake restriction -- An acceleration from a stop should cause the MAF sensor parameter displayed on a scan tool to increase from about 1.1 to 2.9 L/sec at idle to 5 to 9 L/sec at 2,500 RPM. Check for a plugged intake air duct or a dirty air filter element.

If the DTC P0102 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P0102 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0102 appears in the Not Ran Since Code Cleared list, the P0102 diagnostic has not yet run. When the DTC P0102 does not appear in the Not Ran Since Code Cleared list, the P0101 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0102 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

An intermittent malfunction may be caused by a fault in the MAF sensor electrical circuits. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

If you cannot duplicate the DTC P0102, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

### Test Description

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

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and to 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 will determine if the fault is present.

3. Review Freeze Frame data in order to determine when the DTC set. Always record this information.

4. This step checks for an open or short circuit in the MAF sensor signal circuit between the MAF sensor and the PCM.

Step | Action | Value(s) | 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. Start the engine.
2. Install a scan tool.
3. With the throttle closed, select the MAF sensor parameter on the scan tool.

Is the MAF sensor display at the specified value?

1.1-2.9 L/sec

Go to Step 4

Go to Step 3

3 |

1. Turn ON the ignition, leaving the engine OFF.
2. Use the scan tool clear information function.
3. Operate the vehicle within the Freeze Frame conditions as observed.

Is the MAF sensor display at the specified value?

5-9 L/sec at 2,500 RPM

Go to Step 4

Go to Diagnostic Aids

4 |

1. Check for any of the following conditions:

• | Objects blocking the MAF sensor inlet screen

• | Intake manifold vacuum leaks

• | Throttle body vacuum leaks

• | EGR valve leaks

• | A faulty, missing, or incorrectly installed positive crankcase ventilation (PCV) valve

2. Repair as necessary.

Was a repair necessary?

--

Go to Step 11

Go to Step 5

5 |

1. Turn OFF the ignition.
2. Disconnect the MAF sensor connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Measure the voltage from the MAF sensor ignition feed circuit using a DMM connected to ground.

Is the voltage near the specified value?

B+

Go to Step 6

Go to Step 7

6 |

1. Turn OFF the ignition.
2. Reconnect the MAF sensor connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Backprobe the MAF sensor signal circuit at PCM using a DMM.
5. Measure the voltage.

Is the voltage within the specified value?

1.0-1.6 V

Go to Step 10

Go to Step 8

7 |

1. Locate the open or the short circuit in the MAF sensor ignition feed circuit.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 11

--

8 |

1. Check the MAF sensor signal circuit for the following conditions:

• | An open between the PCM and the MAF sensor

• | A short between the PCM and the MAF sensor

• | A poor connection at the MAF sensor

2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 11

Go to Step 9

9 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Is the action complete? | -- | Go to Step 11 | --
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the replacement complete? | -- | Go to Step 11 | --
11 |

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 12

Go to Step 2

12 | 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