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Guides

Guides to the check engine light and trouble codes.

What to do when the light comes on, how to read a code and what individual codes mean, and how to connect an ELM327 adapter to a laptop.

Getting started

  • Check engine light on? First steps before you buy parts
  • Trouble codes: how to read an OBD-II trouble code
  • ELM327 adapters: use one with a Windows, macOS or Linux laptop

Guides to individual codes

  • P0101: mass air flow range/performance
  • P0171: system too lean (Bank 1)
  • P0172: system too rich (Bank 1)
  • P0300: random or multiple cylinder misfire
  • P0401: insufficient EGR flow
  • P0420: catalyst efficiency below threshold
  • P0442: small EVAP system leak
  • P0455: large EVAP system leak
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