Trouble Codes

P0171 System Too Lean Bank 1

Diagnostic Fault Code P0171


Learning poor condition in the fuel mixture control system
Possible causes P0171

  •  Flexible, looped or incorrectly connected flexible vacuum lines
  • At the last amount of fuel in the tank
  • Low fuel pressure.
  • Fuel contamination
  • Fuel injector malfunction.
  • No loose, loose or leaky components of the exhaust system from HO2S to the front
  • Press of vacuum on the intake manifold, throttle body and injector O-rings
  • Possibilities in the air intake system or in the intake ducts of the air
  • No part of the air filter
  • EVAP absorber cracked
  • Disturbation or leakage of rigid fuel vapor pipes
  • Purity in the crankcase ventilation system.

Additional information P0171

• Check whether the correct air filter is used. Check that the oil filler cap is in place and that it is curled. Check if the engine oil dipstick is pressed correctly.
• Some non-standard air filters may set the DTC.
• Some air intake systems, available on the aftermarket, or modification of the intake system may set the DTC.
• Certain non-fabricated components of the exhaust system may set the DTC.


The engine control module (ECM) controls the air / fuel metering system for the best possible combination of driving conditions, fuel economy and emissions. The ECM monitors the heated oxygen sensor (HO2S) signal voltage and regulates the fuel supply depending on the signal voltage in the closed loop state. The change made in the fuel delivery system changes the value of the long-term and short-term adaptive composition (FT) value. Short-term FT values ​​change quickly in response to changes in HO2S voltage signals. These changes precisely adjust the dosing of fuel to the engine. The long-term FT makes approximate adjustments to maintain an optimal air to fuel ratio. The ideal FT values, expressed as a percentage, are close to zero. A positive FT value indicates that the ECM adds fuel to compensate for the lean mixture. A negative FT value indicates that the ECM limits the amount of fuel to compensate for the rich mixture. Fault code P0171 may apply to such car brands as Toyota, Chevrolet, Ford, Nissan, Honda, GMC, Dodge, etc.

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