DTC P0172: Fuel Trim No. 1 (Right Bank) Malfunction (Too Rich)

Perform basic diagnostic procedure. See BASIC DIAGNOSTIC PROCEDURE . Check for loose bolts and/or holes in exhaust system. Repair as required. If exhaust system is sealed and has no loose components, go to next step.
Check for holes, loose bolts and/or disconnected hoses in air intake system. Repair as required. If air intake system is sealed and has no loose or disconnected components, go to next step.
WARNING: Release fuel pressure before removing fuel lines. See FUEL SYSTEM PRESSURE RELEASE in BASIC DIAGNOSTIC PROCEDURES article.

NOTE: During test, if fuel pressure does not increase, squeeze fuel return hose 2-3 times and recheck fuel pressure.
Disconnect fuel delivery hose from fuel filter and connect a fuel pressure gauge between filter and delivery hose. Install fuel filler cap. Start engine and idle with transaxle in Neutral. Check fuel pressure with pressure regulator hose disconnected from intake manifold. See FUEL SYSTEM in SERVICE & ADJUSTMENT SPECIFICATIONS article. If fuel pressure is within specifications, go to next step. If fuel pressure is too high, check for blocked fuel return line or bent hose. If fuel pressure is too low, check for improper fuel pump discharge or blocked fuel supply line.
Check fuel pressure with pressure regulator vacuum hose connected. See FUEL SYSTEM in SERVICE & ADJUSTMENT SPECIFICATIONS article. If fuel pressure is within specifications, go to next step. If fuel pressure is too high, check for faulty pressure regulator, blocked fuel return line or bent hose. If fuel pressure is too low, check for faulty pressure regulator, improper fuel pump discharge or blocked fuel supply line.
WARNING: Release fuel pressure before removing fuel pressure test gauge. See FUEL SYSTEM PRESSURE RELEASE in BASIC DIAGNOSTIC PROCEDURES article.
Remove fuel pressure test gauge and reconnect fuel delivery hose. Turn ignition off. Remove fuel injector(s) on right-side of engine. Inspect injector(s) for clogging. Replace clogged injector(s). If injector(s) is not clogged, go to next step.
Turn ignition off. Disconnect fuel injector electrical connector. Measure fuel injector resistance by measuring across both terminals of fuel injector. If fuel injector resistance is 5-20 ohms, go to next step. If fuel injector resistance is not 5-20 ohms, replace faulty fuel injector.
Start and warm engine to normal operating temperature. Using scan tool, observe engine coolant temperature. If engine coolant temperature is greater than 167°F (75°C), go to next step. If coolant temperature is not greater than 167°F (75°C), replace engine coolant temperature sensor.
Start engine. Operate engine until coolant temperature is greater than 167°F (75°C). Place transaxle in Neutral. Ensure all accessories and A/C are off. Using scan tool, read intake manifold absolute pressure. If pressure is 7.09-12.20 in. Hg with engine idling and 21.65-31.50 in. Hg with ignition on (engine off), go to next step. If pressure is not 7.09-12.20 in. Hg with engine idling and 21.65-31.50 in. Hg with ignition on (engine off), replace intake manifold pressure sensor.
Start engine. Operate engine until coolant temperature is greater than 167°F (75°C). Place transaxle in Neutral. Ensure all accessories and A/C are off. Open and support hood on vehicle. Using a thermometer, measure ambient temperature. Using scan tool, read intake air temperature. Subtract ambient temperature reading from intake air temperature reading. If difference in readings is greater than 14°F (-10°C) and less than 122°F (50°C), contact authorized Subaru dealership because probable cause is deterioration of multiple parts. If difference in readings is not greater than 14°F (-10°C) and not less than 122°F (50°C), check intake air temperature (IAT) sensor circuit. See DTC P0111: INTAKE AIR TEMPERATURE (IAT) SENSOR CIRCUIT RANGE/PERFORMANCE PROBLEM . Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES and VERIFICATION PROCEDURE .