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  .

   Are there holes or loose bolts on exhaust system?

   • Yes: Repair the exhaust system.
   • No: Go to 2  .
2. CHECK 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.

   Measure the fuel pressure. Ref. to MECHANICAL(H4DO)>Fuel Pressure>INSPECTION .

   CAUTION: Release fuel pressure before removing the fuel pressure gauge.

   Is the measured value 340 - 400 kPa (3.5 - 4.1 kg/cm² , 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. Using the Subaru Select Monitor or a general scan tool, read the value of [Coolant Temp.].
   NOTE:

   • Subaru Select Monitor

     For detailed procedures, refer to "Data Monitor". 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. For CVT models, set the select lever to "P" range or "N" range, and for MT models, place the shift lever in the neutral position.
   3. Turn the A/C switch to OFF.
   4. Turn all the accessory switches to OFF.
   5. Using the Subaru Select Monitor or a general scan tool, read the value of [Mass Air Flow].
   NOTE:

   • Subaru Select Monitor

     For detailed procedures, refer to "Data Monitor". 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. For CVT models, set the select lever to "P" range or "N" range, and for MT models, place the 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. Using the Subaru Select Monitor or a general scan tool, read the value of [Intake Air Temp.].
   NOTE:

   • Subaru Select Monitor

     For detailed procedures, refer to "Data Monitor". 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.

   Is the PCV valve free from deformation, crack or other damage?

   • Yes: Repair or replace the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV Valve .
   • No: Go to 8  .
8. CHECK PCV HOSE  .

   Check the PCV hose.

   Is the PCV hose free from deformation, crack or other damage?

   • Yes: Check the PCV hose assembly for cracks, damage or looseness. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV Hose>INSPECTION .
   • No: Repair the poor contact of ECM connector.