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P0171 System too lean (bank 1)

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System too lean (bank 1), readable through chat.

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System
Fuel / air
Component
Fuel trim (air-fuel mixture control)

Symptoms

  • Check engine light on
  • Hard starting
  • Rough or unstable idle
  • Surging or hesitation

Common causes

  • Intake air leak
  • Faulty PCV valve or hose
  • Dirty or faulty mass air flow sensor
  • Low fuel pressure from a weak fuel pump
  • Faulty or clogged fuel injectors
  • Faulty air-fuel ratio sensor
  • Exhaust leak
  • EGR valve stuck open

Guides for this code

Pencil sketch of a Toyota Camry in a garage
Diagnostics & Repair

P0171 on a 2018-2019 Toyota Camry 2.5L: Lean Code Causes and Fixes

JC Landry · Oct 30, 2026

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Answers come from the factory manual for your make, model and year, with the page cited. Join the waitlist and we will email you when a spot opens up.