DTC P0172 System Too Rich (Bank 1): Trouble Symptom

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

Improper idling
Engine stalls.
Poor driving performance

CAUTION: After servicing or replacing faulty parts, perform Clear Memory Mode < Refer to OPERATION , Clear Memory Mode. >, and Inspection Mode < Refer to PROCEDURE , Inspection Mode. >.

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. < Refer to INSPECTION , Fuel Pressure. > CAUTION: Release fuel pressure before removing the fuel pressure gauge.	Is the measured value 340 - 400 kPa (3.5 - 4.1 kg/cm² , 49 - 58 psi)?	Go to step 4 .	Repair the following item. Fuel pressure is too high: Clogged fuel line or bent hose Fuel pressure is too low: Improper fuel pump discharge Clogged fuel line
4 CHECK ENGINE COOLANT TEMPERATURE SENSOR. Start the engine and warm up completely. 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 5 .	Replace the engine coolant temperature sensor. < Refer to ENGINE COOLANT TEMPERATURE SENSOR . >
5 CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR. Start the engine and warm up engine until coolant temperature is higher than 75°C (167°F). For AT models, set the select lever to "P" range or "N" range, and for MT models, place the shift lever in the neutral position. Turn the A/C switch to OFF. Turn all the accessory switches to OFF. 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 6 .	Replace the mass air flow and intake air temperature sensor. < Refer to MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR . >
6 CHECK MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR. Start the engine and warm up engine until coolant temperature is higher than 75°C (167°F). For AT models, set the select lever to "P" range or "N" range, and for MT models, place the shift lever in the neutral position. Turn the A/C switch to OFF. Turn all the accessory switches to OFF. Open the front hood. Measure the ambient temperature. 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 . >