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.

P0171 System too lean (Bank 1)

Can I drive with P0171?

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.

The car usually runs, but it may hesitate, and running lean for a long time can cause misfires and overheat internal parts.

What does P0171 mean?

The engine is getting too much air or too little fuel on bank 1, and the computer has reached its limit trying to correct it. On engines with two banks, P0174 is the same fault on the other side of the engine.

What causes P0171?

Unmetered air from a vacuum leak is the most common cause. If P0174 sets at the same time, look for something shared by both banks.

  1. Vacuum leak from a cracked hose or intake gasket
  2. Dirty or faulty mass airflow (MAF) sensor
  3. Weak fuel pump or clogged fuel filter
  4. Clogged fuel injectors
  5. Leaking PCV valve or hose

How much does it cost to fix P0171?

$50 – $1,000

Vacuum hose: $50–$200. MAF sensor: $150–$450. Fuel pump: $500–$1,000. Start with the cheap checks: inspect hoses and the intake duct for cracks, and try cleaning the MAF sensor before replacing anything. A shop smoke test finds leaks you cannot hear.

What are the symptoms of P0171, and how can I confirm it?

Many cars show no symptoms. Others hesitate, idle rough, or misfire, and a big vacuum leak can hiss. With the engine running, listen around the intake and vacuum hoses. On a scan tool, large positive long-term fuel trims confirm the engine is running lean. Misfire codes and P0101 sometimes appear alongside it.

Will P0171 fail an emissions test, and should I clear it?

It fails any OBD-II based inspection while the light is on, and running lean raises nitrogen oxide emissions. After a repair, clear it and drive normally for several days so the readiness monitors can finish. If P0171 returns, the leak or fuel problem 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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