Trouble codes › P0172

P0172 System Too Rich (Bank 1)

Fuel and air

P0172 means bank 1 is running rich (too much fuel), often from a leaking injector, high fuel pressure or a dirty MAF sensor.

The engine computer has pulled as much fuel out of the mixture on bank 1 as it's allowed, and the oxygen sensor still says it's running rich. Something is adding fuel, or the computer is measuring less air than is really coming in.

Can I keep driving? Yes, but get it fixed soon.

Usually drivable for now, but running rich wastes fuel, fouls spark plugs and can overheat the catalytic converter. Get it checked soon.

Common causes

  1. A leaking fuel injector
  2. Fuel pressure too high (a stuck fuel pressure regulator)
  3. A dirty or failing mass airflow (MAF) sensor reading wrong
  4. A clogged engine air filter
  5. Fuel in the engine oil (from a leaking injector or many short trips) feeding vapor through the PCV system
  6. A faulty engine coolant temperature sensor telling the computer the engine is cold

Symptoms

  • Poor fuel economy
  • Fuel smell or black smoke from the exhaust
  • Rough idle, sometimes misfires or hard starting when hot

What to check first

  1. Check the air filter.
  2. Smell the engine oil: a strong fuel smell points to fuel getting into the oil.
  3. With a scan tool, check the coolant temperature reading on a warm engine (it should be near normal operating temperature, roughly 195-220°F on most engines).
  4. Clean the MAF sensor with MAF cleaner and recheck the fuel trims.
  5. Test fuel pressure, and check whether pressure holds after shut-off: a fast drop can mean a leaking injector.

What does P0172 mean on your vehicle?

The likely cause depends on your engine. iRepair researches your exact year, make, model and engine (service bulletins, recalls and owner reports) and tells you what to check first. Your first 3 questions are free.

Ask iRepair about P0172

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Related codes

General guidance for P0172 on most vehicles. Some makers use the same code a little differently; confirm in the service information for your vehicle, put safety first, and see a professional when in doubt.