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P0172 System too rich (bank 1)

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

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System
Fuel / air
Component
Fuel metering: injectors, air-flow and air/fuel sensors

Symptoms

  • Check engine light
  • Lack of power or hesitation
  • Smell of fuel from the exhaust or the engine oil
  • Poor fuel economy

Common causes

  • Leaking or sticking fuel injector
  • Dirty air filter or restricted intake
  • Faulty mass airflow or air/fuel ratio sensor
  • Fuel pressure higher than specified
  • Fuel diluting the engine oil

Guides for this code

2016-221 Honda Civic sedan in a garage with a floor jack and tires
Diagnostics & Repair

P0172 on a 2016-2021 Honda Civic 1.5T: Running Rich, Causes, Fix

JC Landry · Oct 27, 2026
Honda CR-V (5th-gen)
Diagnostics & Repair

Honda CR-V 1.5T oil dilution: fuel in the oil, P0172 and P0300 codes, and Honda’s software update

JC Landry · Oct 30, 2026

Related terms

  • Oil dilution: Fuel mixed into the engine oil, which thins the oil and makes the oil level on the dipstick rise.
  • Direct injection: A fuel system that sprays fuel directly into each cylinder instead of into the intake port.

Related symptoms

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