DTC P0172: System Too Rich Bank 1: Notes

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

Trouble symptom: 

• Improper idling
• Engine stalls.
• Poor driving performance

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 while disconnecting pressure regulator vacuum hose from intake manifold. Refer to MECHANICAL (STI)>FUEL PRESSURE>INSPECTION .

   NOTE: If fuel pressure does not increase, squeeze the fuel return hose 2 to 3 times, then measure fuel pressure again.

   Is the measured value 284 - 314 kPa (2.9 - 3.2 kg/cm² , 41 - 46 psi)?

   Yes:  Go to  4.

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

4. CHECK FUEL PRESSURE. 

   After connecting the pressure regulator vacuum hose, measure fuel pressure. Refer to MECHANICAL (STI)>FUEL PRESSURE>INSPECTION .

   NOTE:

   • If fuel pressure does not increase, squeeze fuel return hose 2 to 3 times, then measure fuel pressure again.
   • If the measured value at this step is out of specification, check or replace pressure regulator and pressure regulator vacuum hose.

   Is the measured value 230 - 260 kPa (2.4 - 2.7 kg/cm² , 33 - 38 psi)?

   Yes:  Go to  5.

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

5. 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 "Read Current Data For Engine". Refer to ENGINE (DIAGNOSTICS) (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  6.

      No:  Replace the engine coolant temperature sensor. Refer to FUEL INJECTION (FUEL SYSTEMS) (STI)>ENGINE COOLANT 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. 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 "Read Current Data For Engine". Refer to ENGINE (DIAGNOSTIC) (STI)>SUBARU SELECT MONITOR .
      • General scan tool For detailed operation procedures, refer to the general scan tool operation manual.

      Is the value of «Mass Air Flow» 2 - 5 g/s (0.26 - 0.66 lb/m)?

      Yes:  Go to  7.

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

7. 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 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 «Intake Air Temperature» using the Subaru Select Monitor or a general scan tool.
      NOTE:

      • Subaru Select Monitor For detailed operation procedures, refer to "Read Current Data For Engine". Refer to ENGINE (DIAGNOSTICS) (STI)>SUBARU SELECT MONITOR .
      • General scan tool For detailed operation procedures, refer to the general scan tool operation manual.

      Subtract ambient temperature from «Intake Air Temperature». Is the obtained value -10 - 50°C (-18 - 90°F)?

      Yes:  Go to  8.

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

8. CHECK PCV VALVE. 

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

   Is the check result OK?

   Yes:  Repair or replace the PCV valve. Refer to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (STI)>PCV VALVE .

   No:  Go to  9.

9. 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) (STI)>PCV HOSE ASSEMBLY .

   No:  Go to  10.

10. 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) (STI)>PCV HOSE ASSEMBLY .

    No:  Repair the poor contact of ECM connector.