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 Mode Ref. to ENGINE (DIAGNOSTICS) (EXCEPT FOR STI)>Clear Memory Mode>OPERATION , and inspection mode Ref. to ENGINE (DIAGNOSTICS) (EXCEPT FOR STI)>Inspection Mode>PROCEDURE .

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 .

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 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) (EXCEPT FOR STI)>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) (EXCEPT FOR STI)>Fuel Injector .

No: Repair the short circuit to ground in harness between ECM connector and fuel injector connector.
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.
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.
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(EXCEPT FOR STI)>Fuel Pressure>INSPECTION .

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

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) (EXCEPT FOR STI)>Fuel Pump>INSPECTION . Ref. to FUEL INJECTION (FUEL SYSTEMS) (EXCEPT FOR STI)>Fuel Delivery and Evaporation Lines>INSPECTION .
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) (EXCEPT FOR 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 9.

No: Replace the engine coolant temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (EXCEPT FOR STI)>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. For CVT models, set the select lever to "P" range or "N" range, and for MT models, 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 "Current Data Display For Engine". Ref. to ENGINE (DIAGNOSTICS) (EXCEPT FOR 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» 2.0 - 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) (EXCEPT FOR STI)>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. For CVT models, set the select lever to "P" range or "N" range, and for MT models, 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 «IAT Sensor #11» 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) (EXCEPT FOR STI)>Subaru Select Monitor .
  - General scan tool
    For detailed operation procedures, refer to the general scan tool operation manual.
Subtract ambient temperature value from the value of «IAT Sensor #11». 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) (EXCEPT FOR STI)>Mass Air Flow and Intake Air Temperature Sensor .
CHECK FUEL INJECTOR .
Check fuel injector. Ref. to FUEL INJECTION (FUEL SYSTEMS) (EXCEPT FOR STI)>Fuel Injector>INSPECTION .

Is the check result OK?

Yes: Go to 12.

No: Replace the faulty fuel injector. Ref. to FUEL INJECTION (FUEL SYSTEMS) (EXCEPT FOR STI)>Fuel Injector .
CHECK PCV VALVE .
Check the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (EXCEPT FOR STI)>PCV Valve>INSPECTION .

Is the check result OK?

Yes: Repair or replace the PCV valve. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (EXCEPT FOR STI)>PCV Valve .

No: Go to 13.
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. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (EXCEPT FOR STI)>PCV Hose Assembly .

No: Go to 14.
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. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (EXCEPT FOR STI)>PCV Hose Assembly .

No: Repair the poor contact of ECM connector.