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Home >> Subaru >> 2006 >> Legacy GT spec.B >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 11 (Engine Controls - Engine (Diagnostics) (H4SO)) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0172 System Too Rich (Bank 1)

DTC P0172 System Too Rich (Bank 1)

WARNING: This page is about a different variant/trim than selected.

DTC DETECTING CONDITION: 

TROUBLE SYMPTOM: 

CAUTION: After repairing or replacing the defective part, perform the Clear Memory Mode < Ref. to OPERATION , Clear Memory Mode. > and Inspection Mode < Ref. to PROCEDURE , Inspection Mode. >.
DIAGNOSIS 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 FIRE" signs near the working area.
  • Be careful not to spill fuel.

Measure the fuel pressure while disconnecting pressure regulator vacuum hose from intake manifold.
WARNING: 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.
 Is the fuel pressure 284 - 314 kPa (2.9 - 3.2 kgf/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. < Ref. to INSPECTION , Fuel Pressure. >
WARNING: 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 fuel pressure 206 - 235 kPa (2.1 - 2.4 kgf/cm2 , 30 - 34 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 data of engine coolant temperature sensor signal using Subaru Select Monitor or general scan tool.
NOTE:
  • Subaru Select Monitor

    For detailed operation procedure, refer to "READ CURRENT DATA FOR ENGINE". < Ref. to SUBARU SELECT MONITOR . >

  • General scan tool

    For detailed operation procedure, refer to the general scan tool operation manual.

 Is the engine coolant temperature above 60°C (140°F) ? Go to step 6.  Replace the engine coolant temperature sensor. < Ref. 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 greater than 60°C (140°F).
  2. Place the select lever in "N" or "P" position.
  3. Turn the A/C switch to OFF.
  4. Turn all the accessory switches to OFF.
  5. Read the data of mass air flow and intake air temperature sensor signal using Subaru Select Monitor or general scan tool.
NOTE:
  • Subaru Select Monitor

    For detailed operation procedure, refer to "READ CURRENT DATA FOR ENGINE". < Ref. to SUBARU SELECT MONITOR . >

  • General scan tool

    For detailed operation procedure, refer to the general scan tool operation manual.

 Is the measured value 2.1 - 3.4 g/s (0.28 - 0.45 lb/m)? Go to step 7.  Replace the mass air flow and intake air temperature sensor. < Ref. 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 greater than 60°C (140°F).
  2. Place the shift lever in 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 data of mass air flow and intake air temperature sensor signal using Subaru Select Monitor or general scan tool.
NOTE:
  • Subaru Select Monitor

    For detailed operation procedure, refer to "READ CURRENT DATA FOR ENGINE". < Ref. to SUBARU SELECT MONITOR . >

  • General scan tool

    For detailed operation procedure, refer to the general scan tool operation manual.

 Subtract ambient temperature from intake air temperature. Is the obtained value -10 - 50°C (14-122°F)? Replace the ECM. < Ref. to ENGINE CONTROL MODULE (ECM) . > Check the mass air flow and intake air temperature sensor. < Ref. to MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR . >
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