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Home >> Subaru >> 2013 >> Legacy Premium, Automatic CVT Trans >> Repair and Diagnosis >> External Pages >> Different car >> Section 37 (Engine Controls (Diagnostics) (H4DOTC)) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0172 System Too Rich (Bank 1) >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2013 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
DIAGNOSTIC PROCEDURE

Step Check Yes No
1 CHECK EXHAUST SYSTEM.  Are there holes or loose bolts on exhaust system? Repair the exhaust system. Go to step 2. 
2 CHECK AIR INTAKE SYSTEM.  Are there holes, loose bolts or disconnection of hose on air intake system? Repair the air intake system. Go to step 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 while disconnecting pressure regulator vacuum hose from intake manifold. < Refer to INSPECTION , Fuel Pressure. >
CAUTION: Release fuel pressure before removing the fuel pressure gauge.
NOTE: If fuel pressure does not increase, squeeze the fuel return hose 2 to 3 times, then measure fuel pressure again.
 Is the measured value 284 - 314 kPa (2.9 - 3.2 kg/cm2 , 41 - 46 psi)? Go to step 4.  Repair the following item.
Fuel pressure is too high:
  • Clogged fuel return line or bent hose

    Fuel pressure is too low:

  • Improper fuel pump discharge
  • Clogged fuel supply line
4 CHECK FUEL PRESSURE. 
After connecting the pressure regulator vacuum hose, measure fuel pressure. < Refer to INSPECTION , Fuel Pressure. >
CAUTION: Release fuel pressure before removing the fuel pressure gauge.
NOTE:
  • If fuel pressure does not increase, squeeze fuel return hose 2 to 3 times, then measure fuel pressure again.
  • If the measured value at this step is out of specification, check or replace pressure regulator and pressure regulator vacuum hose.
 Is the measured value 230 - 260 kPa (2.35 - 2.65 kg/cm2 , 33 - 38 psi)? Go to step 5.  Repair the following item.
Fuel pressure is too high:
  • Faulty pressure regulator
  • Clogged fuel return line or bent hose

    Fuel pressure is too low:

  • Faulty pressure regulator
  • Improper fuel pump discharge
  • Clogged fuel supply line
5 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 "READ CURRENT DATA FOR ENGINE". < Refer to 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? Go to step 6.  Replace the engine coolant temperature sensor. < Refer to ENGINE COOLANT 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. 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 "READ CURRENT DATA FOR ENGINE". < Refer to 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)? Go to step 7.  Replace the mass air flow and intake air temperature sensor. < Refer to MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR . >
7 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 "READ CURRENT DATA FOR ENGINE". < Refer to 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)? Repair the poor contact of ECM connector. Check the mass air flow and intake air temperature sensor. < Refer to MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR . >
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