P0171 OBD II Trouble CodeOBD-II DTC: System Too Lean (Bank 1)

Symptoms of P0171 OBD II Trouble Code

  • a lack of power
  • detonation (spark knock)
  • rough idle
  • hesitation/surge on acceleration.

Common Causes of P0171 OBD II Trouble Code

  • The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
  • There could be a vacuum leak downstream of the MAF sensor
  • Possible cracked vacuum or PCV line/connection
  • Faulty or stuck open PCV valve
  • Failed or faulty oxygen sensor (bank 1, sensor 1)
  • Sticking/plugged or failed fuel injector
  • Low fuel pressure (possible plugged/dirty fuel filter!)
  • Exhaust leak between engine and first oxygen sensor