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DTC code

P0172

System Too Rich (Bank 1)

Technical guide

Symptoms

  • Black smoke
  • poor fuel economy
  • fuel smell
  • rough idle
  • check engine light
  • sooty spark plugs

Probable causes

  • System too rich bank 1
  • stuck open injector
  • failed MAP sensor
  • faulty ECT sensor (reads cold always)
  • stuck open EVAP purge
  • faulty upstream O2 sensor

Diagnostic steps

  1. Check live O2 readings.
  2. Check MAP sensor.
  3. Test ECT sensor.
  4. Test EVAP purge valve.
  5. Check injector resistance.
  6. Replace faulty component.
Brand-specific notes (Honda)

Honda · Civic/Accord/CRV/Jazz · D15/D16 / R18 / K20

Symptoms

  • Black smoke from exhaust
  • poor fuel economy
  • fuel smell
  • rough idle
  • check engine light
  • spark plugs sooting up

Probable causes

  • Stuck open fuel injector
  • failed MAP sensor giving high pressure reading
  • faulty coolant temperature sensor causing ECM to think engine is cold
  • EVAP purge valve stuck open
  • upstream O2 sensor fault
  • faulty idle air control valve

Diagnostic steps

  1. Check live O2 sensor data - should cycle between 0.1-0.9V normally.
  2. Check MAP sensor reading at idle.
  3. Test fuel injectors - measure resistance (10-13 ohm typically).
  4. Check ECT sensor reading.
  5. Test EVAP purge valve.
  6. Replace upstream O2 sensor if old/sluggish.

Cross-checked technical synthesis (QA). It does not replace the manufacturer's procedure.

Models most reported with this code (NHTSA)

Honda CR-V 43

Count of distinct owner complaints mentioning the code. US data — same engines, same failures.

AI here is a librarian: this page shows only what mechanics confirmed, or says “unknown”. It never suggests a diagnosis — MECCANIC interprets the code, never your car.

0 confirmed cases on P0172

Nothing confirmed yet for this code. No guess is offered on purpose.

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