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DTC P0172: System Too Rich Bank 1: Notes

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

Trouble symptom: 

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>Basic Diagnostic Procedure>PROCEDURE .
  1. CHECK EXHAUST SYSTEM  .

    Check the installation condition of exhaust system.

    Are there holes or loose bolts on exhaust system?

    Yes:  Repair the exhaust system.

    No:  Go to  2.

  2. CHECK AIR INTAKE SYSTEM  .

    Check the installing condition of the air intake system.

    Are there holes, loose bolts or disconnection of hose on air intake system?

    Yes:  Repair the air intake system.

    No:  Go to  3.

  3. CHECK FUEL PRESSURE  .
    WARNING: Place "NO OPEN FLAMES" signs near the working area.
    CAUTION:
    • Be careful not to spill fuel.
    • Before attaching/detaching a fuel pressure gauge, release the fuel pressure.

    Measure the fuel pressure. Ref. to MECHANICAL (H4DO)>Fuel Pressure>INSPECTION .

    Is the measured value 350 - 450 kPa (3.5 - 4.6 kg/cm2 , 50 - 66 psi)?

    Yes:  Go to  4.

    No:  Check the fuel pump and fuel delivery line. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Fuel Pump>INSPECTION . Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Fuel Delivery and Evaporation Lines>INSPECTION .

  4. CHECK ENGINE COOLANT TEMPERATURE SENSOR  .
    1. Start the engine and warm up completely.
    2. Using the Subaru Select Monitor or a general scan tool, read the value of [Coolant Temp.].

      Data Monitor 

      NOTE:
      • SUBARU SELECT MONITOR For detailed operation procedures, refer to the "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>DATA MONITOR .
      • General scan tool For detailed operation procedures, refer to the general scan tool operation manual.

    Is the value of [Coolant Temp.] 75°C (167°F) or more?

    Yes:  Go to  5.

    No:  Replace the engine coolant temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>ENGINE COOLANT TEMPERATURE SENSOR .

  5. CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR  .
    1. Start the engine and warm up engine until coolant temperature is higher than 75°C (167°F).
    2. For CVT models, set the select lever to "P" range or "N" range, and for MT models, place the shift lever in the neutral position.
    3. Turn the A/C switch to OFF.
    4. Turn all the accessory switches to OFF.
    5. Using the Subaru Select Monitor or a general scan tool, read the value of [Mass Air Flow].

      Data Monitor 

      NOTE:
      • SUBARU SELECT MONITOR For detailed operation procedures, refer to the "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>DATA MONITOR .
      • General scan tool For detailed operation procedures, refer to the general scan tool operation manual.

    Is the value of [Mass Air Flow] 2.0 - 5.0 g/s (0.26 - 0.66 lb/m)?

    Yes:  Go to  6.

    No:  Replace the mass air flow and intake air temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR .

  6. CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR  .
    1. Start the engine and warm up engine until coolant temperature is higher than 75°C (167°F).
    2. For CVT models, set the select lever to "P" range or "N" range, and for MT models, place the shift lever in the neutral position.
    3. Turn the A/C switch to OFF.
    4. Turn all the accessory switches to OFF.
    5. Open the front hood.
    6. Measure the ambient temperature.
    7. Using the Subaru Select Monitor or a general scan tool, read the value of [Intake Air Temp.].

      Data Monitor 

      NOTE:
      • SUBARU SELECT MONITOR For detailed operation procedures, refer to the "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>DATA MONITOR .
      • General scan tool For detailed operation procedures, refer to the general scan tool operation manual.

    Subtract ambient temperature from [Intake Air Temp.]. Is the obtained value -10 - 50°C (-18 - 90°F)?

    Yes:  Go to  7.

    No:  Check the mass air flow and intake air temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR .

  7. CHECK PCV VALVE  .

    Check the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV Valve>INSPECTION .

    Does the PCV valve have deformation, cracks or other damages?

    Yes:  Replace the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV VALVE .

    No:  Go to  8.

  8. CHECK PCV HOSE  .

    Check the PCV hose. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV Hose>INSPECTION .

    Does the PCV hose have deformation, cracks or other damages?

    Yes:  Replace the PCV hose. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV HOSE .

    No:  Repair the poor contact of ECM connector.

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