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Home >> Subaru >> 2021 >> Ascent Base >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System (Diagnostics) (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

  1. - 

    DTC detecting condition: 

    Detected when two consecutive driving cycles with fault occur.

    NOTE: When a short period (distance) driving from the engine start to stop is repeated, engine warm-up followed may cause detection of P0172 due to gasoline evaporation within the engine oil and blow-by gas increase.

    Trouble symptom: 

    • Improper idling
    • Engine stalls.
    • Poor driving performance

    Wiring diagram: 

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

G13866306Courtesy of SUBARU OF AMERICA, INC.
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 .
  • When a short period (distance) driving from the engine start to stop is repeated, engine warm-up followed may cause detection of P0172 due to gasoline evaporation within the engine oil and blow-by gas increase.
  1. CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR  .
    1. Turn the ignition switch to OFF.
    2. Disconnect the connector from ECM.
    3. Measure the resistance between ECM connectors.

      Connector & terminal 

      #1 (E159) No. 1 - (E159) No. 2:

      #2 (E159) No. 9 - (E159) No. 10:

      #3 (E159) No. 17 - (E159) No. 18:

      #4 (E159) No. 25 - (E159) No. 26:

    Is the resistance 1.5 Ω (at 23°C (73°F))?

    Yes  : Go to  3.

    No  : Go to  2.

  2. CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR (OPEN)  .
    1. Disconnect the connector from fuel injector.
    2. Measure the resistance of harness between ECM connector and defective fuel injector connector.

      Connector & terminal 

      #1 (E159) No. 1 - (E5) No. 1:

      #1 (E159) No. 2 - (E5) No. 2:

      #2 (E159) No. 9 - (E16) No. 1:

      #2 (E159) No. 10 - (E16) No. 2:

      #3 (E159) No. 17 - (E6) No. 1:

      #3 (E159) No. 18 - (E6) No. 2:

      #4 (E159) No. 25 - (E17) No. 1:

      #4 (E159) No. 26 - (E17) No. 2:

    Is the resistance less than 1 Ω?

    Yes  : Repair or replace the following items.

    • Poor contact of fuel injector connector
    • Defective fuel injector Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>FUEL INJECTOR .

    No  : Repair the open circuit of the harness between the ECM connector and fuel injector connector.

  3. CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR  .

    Measure the resistance between the ECM connector and engine ground.

    Connector & terminal 

    #1 (E159) No. 1 - Engine ground:

    #1 (E159) No. 2 - Engine ground:

    #2 (E159) No. 9 - Engine ground:

    #2 (E159) No. 10 - Engine ground:

    #3 (E159) No. 17 - Engine ground:

    #3 (E159) No. 18 - Engine ground:

    #4 (E159) No. 25 - Engine ground:

    #4 (E159) No. 26 - Engine ground:

    Is the resistance 1 MΩ or more?

    Yes  : Go to  5.

    No  : Go to  4.

  4. CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR (SHORT TO GROUND)  .
    1. Disconnect the connector from fuel injector.
    2. Measure the resistance between ECM connector and engine ground on defective fuel injectors.

      Connector & terminal 

      #1 (E159) No. 1 - Engine ground:

      #1 (E159) No. 2 - Engine ground:

      #2 (E159) No. 9 - Engine ground:

      #2 (E159) No. 10 - Engine ground:

      #3 (E159) No. 17 - Engine ground:

      #3 (E159) No. 18 - Engine ground:

      #4 (E159) No. 25 - Engine ground:

      #4 (E159) No. 26 - Engine ground:

    Is the resistance 1 MΩ or more?

    Yes  : Replace the faulty fuel injector. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>FUEL INJECTOR .

    No  : Repair the short circuit to ground in harness between ECM connector and fuel injector connector.

  5. CHECK EXHAUST SYSTEM  .

    Check the exhaust system.

    Are there holes or loose bolts on exhaust system?

    Yes  : Repair the exhaust system. Ref. to EXHAUST (H4DOTC)>GENERAL DESCRIPTION .

    No  : Go to  6.

  6. CHECK AIR INTAKE SYSTEM  .

    Check the air intake system.

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

    Yes  : Repair the air intake system. Ref. to INTAKE (INDUCTION) (H4DOTC)>GENERAL DESCRIPTION .

    No  : Go to  7.

  7. 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 (H4DOTC)>Fuel Pressure>INSPECTION .

    Is the measured value 340 - 400 kPa (3.5 - 4.1 kgf/cm2 , 49 - 58 psi)?

    Yes  : Go to  8.

    No  : Check the fuel pump and fuel delivery line. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Fuel Pump>INSPECTION . Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Fuel Delivery and Evaporation Lines>INSPECTION .

  8. CHECK ENGINE COOLANT TEMPERATURE SENSOR  .
    1. Start the engine and warm up completely.
    2. Using the Subaru Select Monitor, read the value in [Coolant Temp.].
      NOTE: For detailed operation procedures, refer to "Common (Diagnostics)". Ref. to COMMON (diag)>DATA MONITOR .

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

    Yes  : Go to  9.

    No  : Replace the engine coolant temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>ENGINE COOLANT TEMPERATURE SENSOR .

  9. CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR  .
    1. Start the engine and warm up until the engine coolant temperature exceeds 75°C (167°F).
    2. Place the select lever in "P" range or "N" range.
    3. Turn the A/C switch to OFF.
    4. Turn all the accessory switches to OFF.
    5. Using the Subaru Select Monitor, read the value in [Air Flow Rate from Mass Air Flow Sensor].
      NOTE: For detailed operation procedures, refer to "Common (Diagnostics)". Ref. to COMMON (diag)>DATA MONITOR .

    Is the value of [Air Flow Rate from Mass Air Flow Sensor] 2 - 5 g/s (0.26 - 0.66 lb/min)?

    Yes  : Go to  10.

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

  10. CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR  .
    1. Start the engine and warm up until the engine coolant temperature exceeds 75°C (167°F).
    2. Place the select lever in "P" range or "N" range.
    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, read the value in [Intake Air Temperature (B1-S1)].
      NOTE: For detailed operation procedures, refer to "Common (Diagnostics)". Ref. to COMMON (diag)>DATA MONITOR .

    Subtract ambient temperature from [Intake Air Temperature (B1-S1)]. Is the obtained value -10 - 50 °C (-18 - 90 °F)?

    Yes  : Go to  11.

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

  11. CHECK FUEL INJECTOR  .

    Check fuel injector. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Fuel Injector>INSPECTION .

    Is the check result OK?

    Yes  : Go to  12.

    No  : Replace the faulty fuel injector. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>FUEL INJECTOR .

  12. CHECK PCV VALVE  .

    Check the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>PCV Valve>INSPECTION .

    Is the check result OK?

    Yes  : Go to  13.

    No  : Repair or replace the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>PCV VALVE .

  13. CHECK PCV HOSE ASSEMBLY  .

    Check the PCV hose assembly. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>PCV Hose Assembly>INSPECTION .

    Is the check result OK?

    Yes  : Go to  14.

    No  : Repair or replace the PCV hose assembly. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>PCV HOSE ASSEMBLY .

  14. CHECK PCV HOSE ASSEMBLY  .

    Check the clamp of PCV hose assembly. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>PCV HOSE ASSEMBLY .

    Is the check result OK?

    Yes  : Go to  15.

    No  : Repair or replace the clamp of PCV hose assembly. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>PCV HOSE ASSEMBLY .

  15. CHECK FOR POOR CONTACT  .

    Check for poor contact of ECM connector.

    Is there poor contact of ECM connector?

    Yes  : Repair the poor contact of ECM connector.

    No  : Check the following two items, and when either one matches, replace the engine oil and engine oil filter. Ref. to LUBRICATION (H4DOTC)>ENGINE OIL . Ref. to LUBRICATION (H4DOTC)>OIL FILTER .

    • It is assumed that the user tends to repeat short period (distance) driving from the engine start to stop, and also tends to drive before full engine warmed-up.
    • Compared to other engines of the same type, there is a lot stronger gasoline odor from the engine oil filler neck.

    After the replacement, perform the clear memory of [Engine] using the Subaru Select Monitor or a general scan tool Ref. to COMMON (diag)>CLEAR MEMORY .), and warm up the engine completely.

    After the engine is fully warmed up, perform a no-load idling operation for at least 10 minutes. And then check that the value of the data monitor item, [Short Term Fuel Trim-Bank1] + [Long Term Fuel Trim (B1)], is -20 - 20 %.

    NOTE: When a short period (distance) driving from the engine start to stop is repeated, engine warm-up followed may cause detection of P0172 due to gasoline evaporation within the engine oil and blow-by gas increase.
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