LEMON Manuals: Even more car manuals for everyone
Home >> Mercury >> 2009 >> Mariner Base, 2.5 7, AWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 7 (Engine Controls - Powertrain DTC Charts & Descriptions - (Hybrid)) >> Diagnostic Trouble Code (DTC) Charts and Descriptions >> DTC P0171: System Too Lean (Bank 1)

DTC P0171: System Too Lean (Bank 1)

WARNING: This page is about a different variant/trim than selected.
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:
  • 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
  • Ethanol content in the fuel

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 .