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Home >> Subaru >> 2021 >> WRX Base >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System (Diagnostics) (2.0L) (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

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

Trouble symptom: 

CAUTION:

Wiring diagram: 

Engine Electrical System Refer to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

G13650721Courtesy of SUBARU OF AMERICA, INC.
  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 (E158) No. 11 - (E158) No. 12:

      #2 (E158) No. 23 - (E158) No. 24:

      #3 (E158) No. 35 - (E158) No. 36:

      #4 (E158) No. 47 - (E158) No. 48:

    Is resistance 1.89 - 2.31 Ω at 20°C (68°F)?

    Yes:  Go to  3.

    No:  Go to  2.

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

      Connector & terminal 

      #1 (E158) No. 12 - (E5) No. 1:

      #1 (E158) No. 11 - (E5) No. 2:

      #2 (E158) No. 24 - (E16) No. 1:

      #2 (E158) No. 23 - (E16) No. 2:

      #3 (E158) No. 36 - (E6) No. 1:

      #3 (E158) No. 35 - (E6) No. 2:

      #4 (E158) No. 48 - (E17) No. 1:

      #4 (E158) No. 47 - (E17) No. 2:

    Is the resistance less than 1 Ω?

    Yes:  Repair or replace the following items.

    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 (E158) No. 12 - Engine ground:

    #1 (E158) No. 11 - Engine ground:

    #2 (E158) No. 24 - Engine ground:

    #2 (E158) No. 23 - Engine ground:

    #3 (E158) No. 36 - Engine ground:

    #3 (E158) No. 35 - Engine ground:

    #4 (E158) No. 48 - Engine ground:

    #4 (E158) No. 47 - 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. 
    1. Disconnect the connector from fuel injector.
    2. Measure the resistance between ECM connector and engine ground on defective fuel injectors.

      Connector & terminal 

      #1 (E158) No. 12 - Engine ground:

      #1 (E158) No. 11 - Engine ground:

      #2 (E158) No. 24 - Engine ground:

      #2 (E158) No. 23 - Engine ground:

      #3 (E158) No. 36 - Engine ground:

      #3 (E158) No. 35 - Engine ground:

      #4 (E158) No. 48 - Engine ground:

      #4 (E158) No. 47 - Engine ground:

    Is the resistance 1 MΩ or more?

    Yes:  Replace the faulty fuel injector. Refer to FUEL INJECTION (FUEL SYSTEMS) (W/O STI)>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.

    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.

    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.

    Check the fuel pressure. Refer to INSPECTION .

    Is the check result OK?

    Yes:  Go to  8.

    No:  Check the fuel pump and fuel delivery line. Refer to FUEL INJECTION (FUEL SYSTEMS) (W/O STI)>FUEL PUMP>INSPECTION . Refer to FUEL INJECTION (FUEL SYSTEMS) (W/O STI)>FUEL DELIVERY AND EVAPORATION LINES>INSPECTION .

  8. CHECK ENGINE COOLANT TEMPERATURE SENSOR. 
    1. Start the engine and warm up completely.
    2. Read the value of «Coolant Temp.» using the Subaru Select Monitor or a general scan tool.
      NOTE:
      • Subaru Select Monitor

        For detailed operation procedures, refer to "Current Data Display For Engine Refer to ENGINE (DIAGNOSTICS) (W/O STI)>SUBARU SELECT 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  9.

    No:  Replace the engine coolant temperature sensor. Refer to FUEL INJECTION (FUEL SYSTEMS) (W/O STI)>ENGINE COOLANT TEMPERATURE SENSOR .

  9. 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 gear shift lever in the neutral position.
    3. Turn the A/C switch to OFF.
    4. Turn all the accessory switches to OFF.
    5. Read the value of «Mass Air Flow» using the Subaru Select Monitor or a general scan tool.
      NOTE:
      • Subaru Select Monitor

        For detailed operation procedures, refer to "Current Data Display For Engine". Refer to ENGINE (DIAGNOSTICS) (W/O STI)>SUBARU SELECT MONITOR .

      • General scan tool

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

    Is the value in «Mass Air Flow» 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. Refer to FUEL INJECTION (FUEL SYSTEMS) (W/O STI)>MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR .

  10. 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 gear 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. Read the value of «IAT Sensor #11» using the Subaru Select Monitor or a general scan tool.
      NOTE:
      • Subaru Select Monitor

        For detailed operation procedures, refer to "Current Data Display For Engine". Refer to ENGINE (DIAGNOSTICS) (W/O STI)>SUBARU SELECT MONITOR .

      • General scan tool

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

    Subtract ambient temperature value from the value of «IAT Sensor 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. Refer to FUEL INJECTION (FUEL SYSTEMS) (W/O STI)>MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR .

  11. CHECK FUEL INJECTOR. 

    Check fuel injector. Refer to FUEL INJECTION (FUEL SYSTEMS) (W/O STI)>FUEL INJECTOR>INSPECTION .

    Is the check result OK?

    Yes:  Go to  12.

    No:  Replace the faulty fuel injector. Refer to FUEL INJECTION (FUEL SYSTEMS) (W/O STI)>FUEL INJECTOR .

  12. CHECK PCV VALVE. 

    Check the PCV valve. Refer to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (W/O STI)>PCV VALVE>INSPECTION .

    Is the check result OK?

    Yes:  Go to  13.

    No:  Repair or replace the PCV valve. Refer to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (W/O STI)>PCV VALVE .

  13. CHECK PCV HOSE ASSEMBLY. 

    Check the PCV hose assembly.

    Is the PCV hose assembly deformed, cracked or damaged?

    Yes:  Repair or replace the PCV hose assembly. Refer to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (W/O STI)>PCV HOSE ASSEMBLY .

    No:  Go to  14.

  14. CHECK PCV HOSE ASSEMBLY. 

    Check the clamp of PCV hose assembly.

    Is the clamp of PCV hose assembly damaged or loose?

    Yes:  Repair or replace the clamp of PCV hose assembly. Refer to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (W/O STI)>PCV HOSE ASSEMBLY .

    No:  Repair the poor contact of ECM connector.

  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 

    • 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 Refer to OPERATION , and warm up the engine fully. 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 B1»+«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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