DTC P0171: System Too Lean (Bank 1)

WARNING: This page is about a different car, the 2011 Mercury Milan, 2011 Lincoln MKZ, 2011 Ford Fusion, 2010 Mercury Milan, and 2010 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

P0171 - SYSTEM TOO LEAN (BANK 1)

Description:	The adaptive fuel strategy continuously monitors the fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit. Refer to POWERTRAIN CONTROL SOFTWARE , FUEL TRIM for more information.
Possible Causes:	Fuel System: Ethanol content in the fuel Fuel filter plugged, dirty Damaged or worn fuel pump Leaking fuel pump check valve Leaking/contaminated fuel injectors Low fuel pressure or running out of fuel Evaporative emission (EVAP) canister purge valve is leaking when the canister is clean Fuel supply line restricted Exhaust System: Exhaust leaks in the exhaust manifold gasket or mating gaskets before or near the heated oxygen sensor (HO2S) EGR System: EGR valve tube/gasket leak Intake Air System: Air leaks after the mass air flow (MAF) sensor Vacuum leaks Positive crankcase ventilation (PCV) system is leaking or the valve is stuck open Incorrectly seated engine oil dipstick Intake air turbulence due to incorrect air filter Damaged or contaminated MAF sensor
Diagnostic Aids:	View the freeze frame data to determine the operating conditions when the DTC was set. Observe the LONGFT1 PID. Refer to ADAPTIVE FUEL DIAGNOSTIC TROUBLE CODE (DTCS) DIAGNOSTIC TECHNIQUES , for more information and the appropriate pinpoint test for specific concern identification.
Application	Key On Engine Off	Key On Engine Running	Continuous Memory
All	GO to PINPOINT TEST H .