P0171 — System Too Lean (Bank 1)

P0171 means your engine is getting too much air or not enough fuel on Bank 1. The most common causes are a vacuum leak, dirty MAF sensor, or weak fuel pump.

Cost range: $10–$800. Severity: medium. Safe to drive? Drive short distances only. A long-term lean condition can overheat and destroy your catalytic converter.

Most common causes of P0171

  1. Vacuum leak — Cracked intake hose, bad PCV valve, or torn boot. Smoke-test the intake. ($10–$200)
  2. Dirty MAF sensor — A $8 can of MAF cleaner fixes this in 5 minutes. ($10–$50)
  3. Weak fuel pump or clogged filter — Low fuel pressure starves the engine. ($300–$800)
  4. Failing fuel injector — Clogged or leaking injector skews the air/fuel mix. ($200–$600)
  5. Bad oxygen sensor — Lazy upstream O2 reports incorrect mixture. ($150–$400)

Symptoms drivers report with P0171