ENGINE (DIAGNOSTICS)(H4DOTC) > Diagnostic Procedure with Diagnostic Trouble Code (DTC)

DTC P0102 MASS OR VOLUME AIR FLOW CIRCUIT LOW INPUT

DTC DETECTING CONDITION:

Immediately at fault recognition

TROUBLE SYMPTOM:

• Erroneous idling

• Engine stalls.

• Poor driving performance

CAUTION:

After servicing or replacing faulty parts, perform Clear Memory Mode and Inspection Mode

WIRING DIAGRAM:

STEPCHECKYESNO

1.CHECK CURRENT DATA.

1) Start the engine.

2) Read the data of air flow sensor signal using Subaru Select Monitor or general scan tool.

NOTE:

• Subaru Select Monitor

For detailed operation procedures, refer to “READ CURRENT DATA FOR ENGINE”.

• General scan tool

For detailed operation procedure, refer to the general scan tool operation manual.

Is the voltage less than 0.2 V?

Even if the malfunction indicator light illuminates, 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 may be the cause.

2.CHECK POWER SUPPLY OF MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR.

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 & terminal

(B3) No. 3 (+) — Engine ground (−):

Is the voltage 10 V or more?

Repair the harness and connector.

NOTE:

In this case, repair the following item:

• Open circuit of harness between the main relay and the mass air flow and intake air temperature sensor connector.

• Poor contact of main relay connector

3.CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR CONNECTOR.

1) Turn the ignition switch to OFF.

2) Disconnect the connectors from ECM.

3) Measure the resistance of harness between ECM and the mass air flow and intake air temperature sensor connector.

Connector & terminal

(B135) No. 26 — (B3) No. 5:

Is the resistance less than 1 Ω?

Repair the open circuit of harness between the ECM and mass air flow & intake air temperature sensor connectors.

4.CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR CONNECTOR.

Measure the resistance between ECM and chassis ground.

Connector & terminal

(B135) No. 26 — Chassis ground:

Is the resistance 1 MΩ or more?

Repair the ground short circuit of harness between ECM and the mass air flow and intake air temperature sensor connector.

5.CHECK POOR CONTACT.

Check for poor contact in ECM or the mass air flow and intake air temperature sensor connector.

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

Repair the poor contact in ECM or the mass air flow and intake air temperature sensor connector.

Replace the mass air flow and intake air temperature sensor.