DTC P0171: System Too Lean (Bank 1)

WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 2006 Mercury Mountaineer, 2006 Mercury Monterey, 2006 Mercury Montego, 2006 Mercury Mariner, and 2006 Mercury Grand Marquis. 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: Damaged or leaking fuel pulse damper Fuel filter plugged or dirty Damaged or worn fuel pump Leaking fuel pump check valve Leaking/contaminated fuel injectors Low fuel pressure or running out of fuel EVAP canister purge valve is leaking when the canister is clean Fuel supply line restricted Fuel rail pressure sensor bias Air Induction System: Air leaks after the mass air flow (MAF) sensor Vacuum leaks PCV system is leaking or the valve is stuck open Improperly seated engine oil dipstick Air induction turbulence due to incorrect air filter Exhaust System: Exhaust leaks in the exhaust manifold gasket or mating gaskets before or near the HO2S 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 secondary air injection system or a mechanically stuck valve Air Measurement System: Damaged or contaminated MAF sensor
Diagnostic Aids:	View freeze frame data to determine the operating conditions when the DTC was set. Observe the LONGFT1 and LONGFT2 PIDs. Refer to ADAPTIVE FUEL DTC DIAGNOSTIC TECHNIQUES for more information.
Application	Key On Engine Off	Key On Engine Running	Continuous Memory
All	-	-	GO to Pinpoint Test H .