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..

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 FUEL PRESSURE 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 328 - 358 kPa (3.3 - 3.7 kg/cm² , 48 -52 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 FUEL PRESSURE 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 274 - 304 kPa (2.8 - 3.1 kg/cm² , 40 - 44 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. Start the engine and warm up completely. Read the data of engine coolant temperature sensor signal using Subaru Select Monitor or 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 engine coolant temperature 75°C (167°F) or higher?	Go to step 6 .	Replace the engine coolant temperature sensor. Refer to ENGINE COOLANT TEMPERATURE SENSOR Engine Coolant 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). Place the shift lever in neutral position. Turn the A/C switch to OFF. Turn all the accessory switches to OFF. Read the data of the mass air flow and intake air temperature sensor signal using Subaru Select Monitor or 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 measured value 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 Mass Air Flow and Intake Air Temperature Sensor.
7 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). Place the shift lever in 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 data of the mass air flow and intake air temperature sensor signal using Subaru Select Monitor or 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 temperature. 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 Mass Air Flow and Intake Air Temperature Sensor.