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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: 

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 .

Wiring diagram: 

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

G13202458Courtesy 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 and 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 and 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.

    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 and 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 and 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.

    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.

    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 engine until coolant temperature is higher than 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/m)?

    Yes:  Go to  10.

    No:  Replace the mass air flow and intake air temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>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. 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)].

      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 airflow and intake air temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>MASS AIR FLOW 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:  Repair or replace the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>PCV VALVE .

    No:  Go to  13.

  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:  Repair the poor contact of ECM connector.

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

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