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DTC P0171: System Too Lean (Bank 1)

WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. 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:  Air Measurement System.
  • Mass air flow (MAF) sensor.

Fuel System.
  • Fuel pressure regulator (leaking, faulty).
  • 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 canister is clean).
  • Fuel supply line restricted.
  • Fuel rail pressure sensor (incorrect reading).

Air Induction System.
  • Air leaks after the MAF sensor.
  • Vacuum leaks.
  • PCV system (leak or valve stuck open).
  • Improperly seated engine oil dipstick.

Exhaust System.
  • Exhaust leaks before or near the HO2Ss (exhaust manifold gasket, mating gaskets).

EGR system.
  • EGR valve tube/gasket leak.
  • EVR solenoid vacuum leak.
Diagnostic Aids:  View freeze frame data to determine the operating conditions when the DTC was set. Observe the LONGFT1 PID. Refer to ADAPTIVE FUEL DTCS DIAGNOSTIC TECHNIQUES for more information.
Application  Key On Engine Off  Key On Engine Running  Continuous Memory 
All - - GO to Pinpoint Test H .
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