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 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 normally operating MAF sensor.

### Conditions for Running the DTC

• | The engine is running.

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

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

• | The above conditions are present for greater than 0.5 seconds.

### Conditions for Setting the DTC

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:

• | 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:

• | The secondary ignition wires or coils

• | Any solenoids

• | Any relays

• | Any motors

• | A low minimum air rate may cause this DTC to set during deceleration. Inspect for the following conditions:

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

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

• | Throttle bore and throttle plate coking

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

• | Any unmetered air entering the engine may cause this DTC to set. Inspect for vacuum leaks anywhere downstream of the MAF sensor.

If you suspect that 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. 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.

2. This step tests the signal circuit of the MAF sensor for a short to another 5-volt reference 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. Install a scan tool.
2. Start the engine.
3. With a scan tool observe the frequency parameter of the MAF sensor .

Does the scan tool indicate that the MAF sensor frequency is less than the specified value?

1,200 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 | Inspect the fuse in the ignition 1 voltage circuit of the MAF sensor. Refer to Engine Controls Schematics . Is the fuse open? | -- | Go to Step 14 | Go to Step 5
5 |

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 6

Go to Step 8

6 |

1. Turn OFF the ignition.
2. 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.
3. Start the engine.

Do any additional DTCs set?

--

Go to Step 16

Go to Step 7

7 |

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

Does the test lamp illuminate?

--

Go to Step 18

Go to Step 11

8 | Does the voltage measure less than the specified value? | 4.5 V | Go to Step 10 | Go to Step 9
9 | 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.

Does the voltage measure near the specified value?

0.0 V

Go to Step 12

Go to Step 15

10 |

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 22

Go to Step 12

11 | 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 13 | Go to Step 14
12 | Use a DMM in order to 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 17 | Go to Step 19
13 | 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 22 | --
14 | Important: The ignition 1 voltage circuit of the MAF sensor is spliced to other components on the vehicle. Refer to Power Distribution Schematics in Wiring Systems.

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 22

Go to Step 20

15 | 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 22 | --
16 | 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 22 | --
17 | Repair the circuits that are shorted together. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | --
18 | 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 22 | Go to Step 20
19 | 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 22 | Go to Step 21
20 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Did you complete the replacement? | -- | Go to Step 22 | --
21 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 22 | --
22 |

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 23

Go to Step 2

23 | 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