StopOrDrive

Enter a 5-character code such as P0420, P0301, or P0457.

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Codes starting with P are engine and transmission, B are body, C are chassis, and U are network communication. A 0 as the second character means a generic code shared by all makes; a 1 means a manufacturer-specific code, so its meaning depends on your brand.

A steady check engine light usually means get it checked soon. A flashing check engine light means an active misfire: reduce speed and stop driving as soon as it is safe.

That doesn't look like an OBD-II code

A valid code is one letter (P, B, C, or U) followed by four characters, for example P0420.

P0172 System too rich (Bank 1)

Can I drive with P0172?

Drive soon

OK to drive for now, but get it fixed within days to a couple of weeks, or the damage and the bill can grow.

Not an emergency, but a rich mixture wastes fuel, fouls spark plugs, and can overheat the catalytic converter.

What does P0172 mean?

The engine is getting too much fuel or too little air on bank 1, and the computer can no longer correct it. Bank 1 is the side of the engine with cylinder 1; four-cylinder engines have only one bank. P0175 is the same fault on bank 2.

What causes P0172?

A dirty MAF sensor or a leaking injector is most common. If P0175 sets too, look for a shared cause such as fuel pressure.

  1. Leaking fuel injector
  2. Faulty upstream oxygen or air-fuel sensor
  3. Dirty or faulty mass airflow (MAF) sensor
  4. Fuel pressure too high from a bad regulator
  5. Faulty coolant temperature sensor

How much does it cost to fix P0172?

$100 – $800

MAF cleaning: $10–$15 if you do it yourself. Oxygen sensor: $150–$450. Fuel injector: $250–$600. Clean the MAF sensor and check the air filter before buying parts, since a badly clogged filter can also make the mixture run rich.

What are the symptoms of P0172, and how can I confirm it?

Common signs are worse fuel economy, a fuel smell from the exhaust, black smoke, and a rough idle. On a scan tool, long-term fuel trim well below -10 percent confirms the computer is pulling fuel out. Black, sooty spark plugs and misfire codes often follow if it is ignored.

Will P0172 fail an emissions test, and should I clear it?

It fails any OBD-II based inspection while the light is on, and a rich mixture raises tailpipe emissions. Extra fuel can also overheat the catalytic converter and later set P0420. After a repair, clear the code and drive normally for several days. If P0172 returns, the cause is still there.

Confirm the code yourself

A low-cost scanner lets you read the code, clear it, and see if it comes back before paying for a diagnosis.

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