P0102
C: DTC P0102 - MASS AIR FLOW SENSOR CIRCUIT LOW INPUTDTC DETECTING CONDITION:
- Immediately at fault recognition.
TROUBLE SYMPTOM:
- Erroneous idling.
- Engine stalls.
- Poor driving performance.
CAUTION: After repair or replacement of faulty parts, conduct CLEAR MEMORY and INSPECTION MODES. Clearing Diagnostic Trouble Codes
WIRING DIAGRAM
10C1: CONNECT SUBARU SELECT MONITOR OR THE OBD-II GENERAL CAN TOOL, AND READ DATA.
1) Turn ignition switch to OFF.
2) Connect Subaru Select Monitor or the OBD-II general scan tool to data link connector.
3) Turn ignition switch to ON and Subaru Select Monitor or the OBD-II general scan tool switch to ON.
4) Start engine.
5) Read data of mass air flow sensor signal using Subaru Select Monitor or OBD-II general scan tool.
NOTE:
- Select Monitor. For detailed operation procedure, refer to the READ CURRENT DATA SHOWN ON DISPLAY FOR ENGINE".
- OBD-II general scan tool. For detailed operation procedure, refer to the OBD-II General Scan Tool procedures.
CHECK: Is the value equal to or more than 0 g/sec (0 lb/mm) or 0.3 V and equal to or less than 186 g/sec (25 lb/mm) or 5.0 V?
YES: Even if MIL lights up, the circuit has returned to a normal condition at this time. A temporary poor contact of the connector or harness may be the cause. Repair harness or connector in the mass air flow sensor.
NOTE: In this case, repair the following:
- Open or ground short circuit in harness between mass air flow sensor and ECM connector
- Poor contact in mass air flow sensor or ECM connector.
NO: Go to step 10C2.
10C2: CHECK INPUT SIGNAL FOR ECM.
Connector & Terminal (B136) No.5 (+) - Chassis Ground (-):
Measure voltage between ECM connector and chassis ground while engine is idling.
CHECK: Is the voltage less than 0.3 V?
YES: Go to step 10C4.
NO: Go to step 10C3.
10C3: CHECK INPUT SIGNAL FOR ECM. (USING SUBARU SELECT MONITOR.)
Measure voltage between ECM connector and chassis ground while engine is idling.
CHECK: Does the voltage change more than 0.3 V by shaking harness and connector of ECM while monitoring the value with Subaru Select Monitor?
YES: Repair poor contact in ECM connector.
NO: Contact with Subaru of America (Subaru of America (SOA)) service.
NOTE: Inspection by Subaru of America's Subaru of America's DTM is required, because probable cause is deterioration of multiple parts.
10C4: CHECK POWER SUPPLY TO MASS AIR FLOW SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from mass air flow sensor.
3) Turn ignition switch to ON.
Connector & Terminal (E26) No.2 (+) - Engine Ground (-):
4) Measure voltage between mass air flow sensor connector and engine ground.
CHECK: Is the voltage more than 10 V?
YES: Go to step 10C5.
NO: Repair harness and connector.
NOTE: In this case, repair the following:
- Open or ground short circuit in harness between main relay and mass air flow sensor connector.
- Poor contact in main relay connector.
- Poor contact in coupling connector (B21).
10C5: CHECK POWER SUPPLY TO MASS AIR FLOW SENSOR.
Connector & Terminal (E26) No.4 (+) - Engine Ground (-):
Measure voltage between mass air flow sensor connector and engine ground.
CHECK: Is the voltage more than 4 V?
YES: Go to step 10C6.
NO: Repair harness and connector.
NOTE: In this case, repair the following:
- Open or ground short circuit in harness between ECM and mass air flow sensor connector
- Poor contact in ECM connector
- Poor contact in coupling connector (B21)
10C6: CHECK HARNESS BETWEEN ECM ND MASS AIR FLOW SENSOR CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from ECM.
Connector & Terminal (B136) No.5 - (E26) No.5:
3) Measure resistance of harness between ECM and mass air flow sensor connector.
CHECK: Is the resistance less than 1 Ohm?
YES: Go to step 10C7
NO: Repair harness and connector
NOTE: In this case, repair the following:
- Open circuit in harness between ECM and mass air flow sensor connector
- Poor contact in mass air flow sensor connector
- Poor contact in ECM connector
- Poor contact in coupling connector (B21)
10C7: CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW SENSOR CONNECTOR.
Connector & Terminal (B136) No.8 - (E26) No.3:
Measure resistance of harness between ECM and mass air flow sensor connector.
CHECK: Is the resistance less than 1 Ohm?
YES: Go to step 10C8.
NO: Repair harness and connector.
NOTE: In this case, repair the following;
- Open circuit in harness between ECM and mass air flow sensor connector
- Poor contact in mass air flow sensor connector
- Poor contact in ECM connector
- Poor contact in coupling connector (B21)
10C8: CHECK HARNESS BETWEEN ECM AND MASS AIR FLOW SENSOR CONNECTOR.
Connector And Terminal (B136) No. 5 - Chassis Ground:
Measure resistance of harness between ECM connector and chassis ground.
CHECK: Is the resistance more than 1 Mohm?
YES: Replace mass air flow sensor.
NO: Repair ground short circuit in harness between ECM and mass air flow sensor connector.