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 condition.

The MAF sensor has:

• | An ignition 1 voltage circuit

• | A ground circuit

• | 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 frequency will vary within a range of around 2,000 Hertz at idle to about 10,000 Hertz at maximum engine load. DTC P0102 will set if the PCM detects a frequency signal lower than the possible range of a properly operating MAF sensor.

### Conditions for Running the DTC

• | The engine is running.

• | The idle air control (IAC) position is more than 2 counts.

• | The ignition 1 signal is more than 8 volts.

• | The above conditions are met for more than 0.5 second.

### Conditions for Setting the DTC

The PCM detects that the MAF sensor frequency signal is less than 1,200 Hz.

### 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:

• | An incorrectly routed harness--Inspect the harness of the MAF sensor in order to verify that it is not routed too close to the following components:

- | The secondary ignition wires or coils

- | Any solenoids

- | Any relays

- | Any motors

• | A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration.

• | A wide open throttle (WOT)acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 4-7 g/s at idle to 130 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 resistance of 20 ohms or more on the ground circuit of the MAF sensor can cause this DTC to set.

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

If the condition is intermittent, refer to Intermittent Conditions .

### 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 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.

3. This step tests the signal circuit of the MAF sensor for a short to another 5-volt reference circuit.

4. This step verifies that the signal circuit is not shorted to any other PCM circuit.

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. Start the engine.
2. Observe the MAF sensor frequency with a scan tool .

Is the MAF sensor frequency less than the specified value?

1200 Hz

Go to Step 4

Go to Step 3

3 |

1. Observe 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. Observe the MAF sensor frequency with a scan tool.
2. Move the harness and the connector of the MAF sensor.

Does the movement of the harness or the connector affect the MAF sensor frequency?

--

Go to Step 25

Go to Step 5

5 |

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

• | A restricted or collapsed air intake duct

• | A dirty or deteriorating air filter element

• | Any objects blocking the air inlet screen of the MAF sensor

• | Any debris on the sensing elements of the MAF sensor

• | A restricted exhaust system

• | Any vacuum leak downstream of the MAF sensor

• | A MAF sensor that is installed backwards

Did you find and correct the condition?

--

Go to Step 30

Go to Step 6

6 | Inspect the fuse in the ignition 1 voltage circuit of the MAF sensor. Is the fuse open? | -- | Go to Step 12 | Go to Step 7
7 |

1. Disconnect the harness connector of the MAF sensor. Refer to Mass Airflow Sensor Replacement .
2. Turn ON the ignition, with the engine OFF.
3. 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 8

Go to Step 18

8 | 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 9 | Go to Step 19
9 | Measure the voltage from the signal circuit of the MAF sensor to a good ground. Refer to Circuit Testing in Wiring Systems. Is the voltage near the specified value? | 5.0 V | Go to Step 10 | Go to Step 11
10 |

1. Connect a 3-amp fused jumper wire between the signal circuit of the MAF sensor and a good ground. Refer to Circuit Testing in Wiring Systems.
2. Start the engine.

Do any additional DTCs set?

--

Go to Step 23

Go to Step 26

11 | Is the voltage less than the specified value? | 4.5 V | Go to Step 13 | Go to Step 15
12 | Important:: The ignition 1 voltage circuit of the MAF sensor is spliced to other components of the vehicle. Test for continuity between the ignition 1 voltage circuit of the MAF sensor and ground. Refer to Circuit Testing in Wiring Systems. Does the DMM indicate continuity? | -- | Go to Step 17 | Go to Step 26
13 |

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

• | An open circuit--Refer to Circuit Testing in Wiring Systems.

Does the DMM indicate continuity?

--

Go to Step 14

Go to Step 20

14 | Test for continuity from the signal circuit of the MAF sensor to ground. Refer to Circuit Testing in Wiring Systems. Does the DMM indicate continuity? | -- | Go to Step 21 | Go to Step 16
15 | Important:: Disconnecting the PCM connectors may eliminate the short to voltage if the signal circuit is shorted to another PCM circuit.

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. Refer to Circuit Testing in Wiring Systems.

Is the voltage near the specified value?

0.0 V

Go to Step 16

Go to Step 22

16 | Test for continuity at the harness connector of the PCM from the signal circuit of the MAF sensor to all other circuits at both PCM connectors. Refer to Circuit Testing in Wiring Systems. Does the DMM indicate continuity between any other circuit? | -- | Go to Step 24 | Go to Step 27
17 |

1. Repair the short to ground 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 30

--

18 | Repair the open in the ignition 1 voltage circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 30 | --
19 | 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 30 | --
20 | Repair the high resistance or an open in the signal circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 30 | --
21 | Repair the short to ground in the signal circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 30 | --
22 | 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 30 | --
23 | Repair the short between the signal circuit of the MAF sensor and the circuit for which the DTC set. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 30 | --
24 | Repair the circuits that are shorted together. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 30 | --
25 | Repair the harness or the connections as needed. Refer to Wiring Repairs and to Connector Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 30 | --
26 | Test for an intermittent and for a poor connection at the MAF sensor. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 30 | Go to Step 28
27 | Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 30 | Go to Step 29
28 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Did you complete the replacement? | -- | Go to Step 30 | --
29 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 30 | --
30 |

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 31

Go to Step 2

31 | 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