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

CAUTION:

After servicing or replacing faulty parts, perform Clear Memory Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>Clear Memory Mode . and Inspection Mode Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>Inspection Mode .
Use the check board when measuring the ECM terminal voltage and resistance.

Wiring diagram:

Engine Electrical System Ref. to WIRING SYSTEM>Engine Electrical System>WIRING DIAGRAM .

Fig 1: System Too Rich Bank 1 - Wiring Diagram

Courtesy of SUBARU OF AMERICA, INC.

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 the resistance 1.89 - 2.31 Ω (at 20°C (68°F))?
- Yes: Go to 3.
- No: Go to 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.
  - Poor contact of fuel injector connector
  - Defective fuel injector Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Fuel Injector .
- No: Repair the open circuit of the harness between the ECM connector and fuel injector connector.
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.
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. 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.
CHECK EXHAUST SYSTEM.
Are there holes or loose bolts on exhaust system?
- Yes: Repair the exhaust system.
- No: Go to 6.
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 7.
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(H4DOTC)>Fuel Pressure>INSPECTION .

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

Is the measured value 328 - 358 kPa (3.3 - 3.7 kgf/cm² , 48 - 52 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 .
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) (H4DOTC)>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. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Engine Coolant Temperature Sensor .
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 or a general scan tool, read the value of [Air Flow Rate from Mass Air Flow Sensor].
  NOTE:
  - Subaru Select Monitor
    For detailed procedures, refer to "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>Subaru Select Monitor .
  - General scan tool
    For detailed operation procedures, refer to the general scan tool operation manual.
Is the value of [Air Flow Rate from Mass Air Flow Sensor] 2.0 - 5.0 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 .
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 or a general scan tool, read the value of [Intake Air Temperature (B1-S1)].
  NOTE:
  - Subaru Select Monitor
    For detailed procedures, refer to "Data Monitor". Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>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 (B1-S1)]. 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. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Mass Air Flow and Intake Air Temperature Sensor .
CHECK FUEL INJECTOR.
Check fuel injector. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Fuel Injector>INSPECTION .

Are fuel injectors OK?
- Yes: Repair the poor contact of ECM connector.
- No: Replace the faulty fuel injector. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Fuel Injector .
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) (H4DOTC)>PCV Valve .
- No: Go to 13.
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) (H4DOTC)>PCV Hose Assembly .
- No: Go to 14.
CHECK PCV HOSE.
Check the PCV hose.

Check the clamp of PCV hose assembly for damage or looseness.
- Yes: Repair or replace the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DOTC)>PCV Valve .
- No: Repair the poor contact of ECM connector.