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Home >> Subaru >> 2020 >> Crosstrek Base, Automatic CVT Trans >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 24 (Engine Control System (Diagnostics) (HEV) (2 Of 4)) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0172: System Too Rich Bank 1 >> Notes

DTC P0172: System Too Rich Bank 1: Notes

WARNING: This page is about a different variant/trim than selected.
  1. - 

    DTC detecting condition: 

    Detected when two consecutive driving cycles with fault occur.

    Trouble symptom: 

G13615236Courtesy of SUBARU OF AMERICA, INC.
  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 (EXCEPT FOR HEV))>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 (HEV))>FUEL PUMP>INSPECTION . Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO (HEV))>FUEL DELIVERY AND EVAPORATION LINES>INSPECTION .

  4. CHECK ENGINE COOLANT TEMPERATURE SENSOR  .
    1. Turn the ignition switch to ON.
    2. Navigate to Inspection Mode for measuring Exhaust Gas. Ref. to P-HEV HYBRID POWERTRAIN CONTROL (DIAGNOSTICS)>WORK SUPPORT>OPERATION>SERVICE MODE .
      NOTE: If it is necessary to run the engine for 10 minutes or more, fasten the driver's seat belt.
    3. Start the engine and warm up completely.
    4. Using the Subaru Select Monitor, read the value in [Engine Coolant Temperature].
      NOTE: For detailed operation procedures, refer to "Common (Diagnostics)". Ref. to COMMON (DIAG)>DATA MONITOR .

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

    Yes:  Go to  5.

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

  5. CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR  .
    1. Turn the ignition switch to ON.
    2. Navigate to Inspection Mode for measuring Exhaust Gas. Ref. to P-HEV HYBRID POWERTRAIN CONTROL (DIAGNOSTICS)>WORK SUPPORT>OPERATION>SERVICE MODE .
      NOTE: If it is necessary to run the engine for 10 minutes or more, fasten the driver's seat belt.
    3. Start the engine.
    4. Warm up the engine until coolant temperature is higher than 75°C (167°F).
    5. Place the select lever in "P" range or "N" range.
    6. Turn the A/C switch to OFF.
    7. Turn all the accessory switches to OFF.
    8. 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] 2 - 5 [g/s] (0.26 - 0.66 lb/min)?

    Yes:  Go to  6.

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

  6. CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR  .
    1. Turn the ignition switch to ON.
    2. Navigate to Inspection Mode for measuring Exhaust Gas. Ref. to P-HEV HYBRID POWERTRAIN CONTROL (DIAGNOSTICS)>WORK SUPPORT>OPERATION>SERVICE MODE .
      NOTE: If it is necessary to run the engine for 10 minutes or more, fasten the driver's seat belt.
    3. Start the engine.
    4. Warm up the engine until coolant temperature is higher than 75°C (167°F).
    5. Place the select lever in "P" range or "N" range.
    6. Turn the A/C switch to OFF.
    7. Turn all the accessory switches to OFF.
    8. Open the front hood.
    9. Measure the ambient temperature.
    10. Using the Subaru Select Monitor, read the value in [Intake Air Temp.].
      NOTE: For detailed operation procedures, refer to "Common (Diagnostics)". Ref. to COMMON (DIAG)>DATA MONITOR .

      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 (HEV))>MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR>INSPECTION .

  7. CHECK PCV VALVE  .

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

    Is the check result OK?

    Yes:  Go to  8.

    No:  Replace the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO (HEV))>PCV VALVE .

  8. CHECK PCV HOSE  .

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

    Is the check result OK?

    Yes:  Repair the poor contact of ECM connector.

    No:  Replace the PCV hose. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO (HEV))>PCV HOSE .

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