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Home >> Subaru >> 2023 >> Outback Base >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System (2.5L) (Diagnostics) (2 Of 4) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0172: System Too Rich Bank 1 >> Notes

DTC P0172: System Too Rich Bank 1: Notes

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

NOTE: When a short period (distance) driving from the engine start to stop is repeated, engine warm-up followed may cause detection of P0172 due to gasoline evaporation within the engine oil and blow-by gas increase.

Trouble symptom: 

NOTE:
  • After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .
  • When a short period (distance) driving from the engine start to stop is repeated, engine warm-up followed may cause detection of P0172 due to gasoline evaporation within the engine oil and blow-by gas increase.
  1. CHECK EXHAUST SYSTEM  .

    Check exhaust system parts.

    Are there holes or loose bolts on exhaust system?

    Yes:  Repair the exhaust system. Ref. to EXHAUST (H4DO)>GENERAL DESCRIPTION .

    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. Ref. to INTAKE (INDUCTION) (H4DO)>GENERAL DESCRIPTION .

    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.

    Check the fuel pressure. Ref. to MECHANICAL (H4DO)>FUEL PRESSURE .

    Is the check result OK?

    Yes:  Go to  4.

    No:  Check the fuel pump and fuel delivery line. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>FUEL PUMP ASSEMBLY . Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>FUEL DELIVERY AND EVAPORATION LINES .

  4. CHECK ENGINE COOLANT TEMPERATURE SENSOR (OUTLET)  .
    1. Start the engine and warm up completely.
    2. Using the Subaru Select Monitor, read the value in [Engine Coolant Temperature 1].
    NOTE: For detailed operation procedures, refer to "COMMON (DIAGNOSTICS)". Ref. to COMMON (DIAGNOSTICS)>DATA MONITOR .

    Is the value of [Engine Coolant Temperature 1] 75 [°C] (167°F) or more?

    Yes:  Go to  5.

    No:  Replace the engine coolant temperature sensor (outlet). 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 until the engine coolant temperature exceeds 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, read the value in [Mass Air Flow].
    NOTE: For detailed operation procedures, refer to "COMMON (DIAGNOSTICS)". Ref. to COMMON (DIAGNOSTICS)>DATA MONITOR .

    Is the value of [Mass Air Flow] 2 - 5 [g/s] (0.26 - 0.66 lb/min)?

    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 until the engine coolant temperature exceeds 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, read the value in [Intake Air Temp.].
    NOTE: For detailed operation procedures, refer to "COMMON (DIAGNOSTICS)". Ref. to COMMON (DIAGNOSTICS)>DATA MONITOR .

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

    Yes:  Go to  7.

    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 .

  7. CHECK PCV HOSE  .

    Check PCV hose No. 1. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV HOSE .

    Is the check result OK?

    Yes:  Go to  8.

    No:  Repair or replace PCV hose No. 1. Ref. to EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) (H4DO)>PCV HOSE .

  8. CHECK FOR POOR CONTACT  .

    Check for poor contact of ECM connector.

    Is there poor contact of ECM connector?

    Yes:  Repair the poor contact of ECM connector.

    No:  Check the following two items, and when either one matches, replace the engine oil and engine oil filter. Ref. to LUBRICATION (H4DO)>ENGINE OIL>REPLACEMENT . Ref. to LUBRICATION (H4DO)>OIL FILTER>REMOVAL .

    • It is assumed that the user tends to repeat short period (distance) driving from the engine start to stop, and also tends to drive before full engine warmed-up.
    • Compared to other engines of the same type, there is a lot stronger gasoline odor from the engine oil filler neck.

    After the replacement, perform the clear memory of [Engine] using the Subaru Select Monitor or a general scan tool (Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY .), and warm up the engine completely.

    After the engine is fully warmed up, perform a no-load idling operation for at least 10 minutes. And then check that the value of the data monitor item, [Short Term Fuel Trim-Bank1] + [Long Term Fuel Trim (B1)], is -20 - 20 %.

    NOTE: When a short period (distance) driving from the engine start to stop is repeated, engine warm-up followed may cause detection of P0172 due to gasoline evaporation within the engine oil and blow-by gas increase.
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