DTC P0171: System Too Lean (Bank 1)

WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2005 Mercury Sable, 2005 Mercury Mountaineer, 2005 Mercury Monterey, 2005 Mercury Montego, and 2005 Mercury Mariner. 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 FUEL TRIM for more information.
Possible Causes:	Fuel System: Fuel pressure regulator (leaking or damaged) Fuel filter plugged, dirty Fuel pump (weak, check valve leaking) Leaking/contaminated fuel injectors Low fuel pressure or running out of fuel EVAP canister purge valve leaking (when the canister is clean) Fuel supply line restricted Fuel rail pressure sensor (incorrect reading) Air Induction System: Air leaks after the mass air flow (MAF) sensor Vacuum leaks. PCV system (leak or valve stuck open) Improperly seated engine oil dipstick Exhaust System: Exhaust leaks before or near the HO2S (exhaust manifold gasket, mating gaskets) EGR System: Vacuum hose disconnected on exhaust gas recirculation (EGR) system module (ESM) applications EGR valve tube/gasket leak EVR solenoid vacuum leak Secondary Air Injection: Damaged/malfunctioning secondary air injection system (mechanically stuck valve) Air Measurement System: MAF sensor (contaminated or damaged)
Diagnostic Aids:	View freeze frame data to determine the operating conditions when the DTC was set. Observe the LONGFT1 and LONGFT2 PID(s). Refer to ADAPTIVE FUEL DTC DIAGNOSTIC TECHNIQUES for more information.
Application	Key On Engine Off	Key On Engine Running	Continuous Memory
All	-	-	GO to H: Fuel Control STEP H16.