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System Too Lean (Bank 1)

P0171  means that an oxygen sensor in bank 1 has detected a lean condition (too much oxygen in the exhaust).

On vehicles equipped with two blocks (V6 V8 V10), bank 1 is the side of the engine that has cylinder #1. The P0171 is a one of the most common fault codes that triggers the check engine light


Most Common Causes

  • Faulty oxygen sensor
  • Dirty or faulty mass airflow sensor
  • Vacuum leaks
  • Weak fuel pump
  • Clogged or dirty fuel injectors
  • Clogged fuel filter
  • Exhaust leak
  • Faulty air-fuel ratio sensor

DTC Group

Powertrain, Engine, Transmission


Generic OBD2 Code

DTC System

Fuel & Air Metering