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 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 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)>Fuel Pressure>INSPECTION

   Is the measured value 340 - 400 kPa (3.5 - 4.1 kg/C² , 49 - 58 psi)?

   Yes:  Go to  4

   No:  Check the fuel pump and fuel delivery line. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Fuel Pump>INSPECTION Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>Fuel Delivery and Evaporation Lines>INSPECTION

4. 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". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>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  5

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

5. 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. 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". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>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» 2.0 - 5.0 g/s (0.26 - 0.66 lb/m)?

   Yes:  Go to  6

   No:  Replace the mass air flow and intake air temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>MASS AIR FLOW AND INTAKE AIR 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 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. Read the value of «Intake Air 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". Ref. to ENGINE (DIAGNOSTICS) (H4DO)>SUBARU SELECT MONITOR

      • General scan tool

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

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

   Yes:  Repair the poor contact of ECM connector.

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

7. CHECK PCV VALVE. 

   Check the PCV valve.

   Check that the PCV valve has no deformation, cracks or other damages.

   Yes:  Repair or replace the PCV valve.

   No:  Go to  8

8. CHECK PCV HOSE. 

   Check the PCV hose.

   Check the PCV hose assembly for cracks, damage or looseness.

   Yes:  Repair or replace the PCV hose.

   No:  Repair the poor contact of ECM connector.