P0172 System Too Rich (Bank 1)

Powertrain Severity: Moderate Generic OBD-II

The engine computer is removing a lot of fuel on bank 1 because the mixture is too rich.

Common causes

  • Leaking injector
  • High fuel pressure
  • Faulty MAF or coolant sensor
  • Clogged air filter
  • Oil contaminated with fuel

Symptoms

  • Check engine light
  • Fuel smell
  • Black smoke
  • Poor fuel economy

What to check

  1. Check fuel trims
  2. Check fuel pressure regulation
  3. Inspect air filter
  4. Test injectors for leaks

Manufacturers may add their own detail to generic codes. If your vehicle shows a different description for P0172, follow the service information for that make and model.

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