DTC P0102: Mass Or Volume Air Flow Sensor "A" Circuit Low: Notes

DTC detecting condition:

Immediately at fault recognition

Trouble symptom:

Improper idling
Engine stalls.
Poor driving performance

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE CHECK BOARD .

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

Wiring diagram:

Engine Electrical System Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM .

Courtesy of SUBARU OF AMERICA, INC.

CHECK DATA MONITOR.
1. Start the engine.
2. Using the Subaru Select Monitor, read the value in [Mass Air Flow].
  NOTE: For detailed operation procedures, refer to "Common (Diagnostics)". Ref. to COMMON (DIAG)>DATA MONITOR .
Is the value of [Mass Air Flow] 0 g/s (0 oz/s)?

Yes : Go to 2.

No : Even if DTC is detected, the circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again.

NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.
CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR POWER SUPPLY.
1. Turn the ignition switch to OFF.
2. Disconnect the connector from the mass air flow and intake air temperature sensor.
3. Turn the ignition switch to ON.
4. Measure the voltage between mass air flow and intake air temperature sensor connector and engine ground.
  Connector and terminal.
  
  (B3) No. 3 (+) - Engine ground (-):
Is the voltage 4.5 V or more?

Yes : Go to 3.

No : Repair the open circuit of harness between ECM connector and the mass air flow and intake air temperature sensor connector.
CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR CONNECTOR (OPEN).
1. Turn the ignition switch to OFF.
2. Disconnect the connector from ECM.
3. Measure the resistance of harness between ECM connector and the mass air flow and intake air temperature sensor connector.
  Connector and terminal.
  
  (B134) No. 63 - (B3) No. 1:
Is the resistance less than 1 Ω?

Yes : Go to 4.

No : Repair the open circuit of harness between ECM connector and the mass air flow and intake air temperature sensor connector.
CHECK HARNESS BETWEEN ECM AND AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR CONNECTOR (SHORT TO GROUND).
Measure the resistance between the ECM connector and engine ground.

Connector and terminal.

(B134) No. 63 - Engine ground:

Is the resistance 1 MΩ or more?

Yes : Go to 5.

No : Repair the ground short circuit of harness between ECM connector and the mass air flow and intake air temperature sensor connector.
CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR (SHORT TO POWER SUPPLY).
1. Turn the ignition switch to ON.
2. Measure the voltage between ECM connector and engine ground.
  Connector and terminal.
  
  (B134) No. 63 (+) - Engine ground (-):
Is the value of [Air Flow Sensor Voltage] 5 V or more?

Yes : Repair the short circuit of harness to power supply between ECM connector and the mass air flow and intake air temperature sensor connector.

No : Go to 6.
CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR (OPEN).
1. Turn the ignition switch to OFF.
2. Connect the connector to ECM.
3. Measure the resistance of harness between mass air flow and intake air temperature sensor connector and engine ground.
  Connector and terminal.
  
  (B3) No. 2 - Engine ground:
Is the resistance less than 5 Ω?

Yes : Go to 7.

No : In this case, repair the following item:
- Open circuit in harness between ECM connector and mass air flow and intake air temperature sensor connector
- Poor contact of ECM connector
CHECK FOR POOR CONTACT.
Check for poor contact of ECM and mass air flow and intake air temperature sensor connector.

Is there poor contact of ECM or mass air flow and intake air temperature sensor connector?

Yes : Repair the poor contact of ECM or mass air flow and intake air temperature sensor connector.

No : Replace the mass air flow and intake air temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR .