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P0171 Diagnostic Trouble Code

Technical description

The engine is running lean on bank 1, meaning the air to fuel ratio is biased towards air.

What P0171 really means

Over time when the engine wears, parts break, or if measuring sensors become faulty, the computer can make corrections by lengthening the on time for the fuel injectors to richen up the mixture.This code can also be accompanied by a P0174, which will identify bank 2 as lean.The ideal stoichiometric ratio is 14.7 parts of air to 1 part of fuel, which allows a good mixture of fuel economy, performance and lower emissions during combustion.

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What are the symptoms for a P0171 code?

Generally, a lean code will cause the engine to run poorly, which the driver will notice as a high idle, a misfire, a lack of power, or even engine stalling, and this may happen before the check engine light has turned on. What’s more, these symptoms will be more noticeable at lower speeds and RPMs. The engine can cope with lean problems at higher speeds because demand is greater for air.

What is the severity of a P0171 code?

Critical. A diagnostic check should be run immediately to pinpoint the exact issue.

What repairs are required for a P0171 code?

There is a long list of reasons why the engine runs lean, and a good mechanic needs time to figure out the problem. Unlike rich issues the problem can be on either side of the mixture – too much air or not enough fuel. To be sure, there are some simple answers here – a broken vacuum hose will let in air that the computer cannot account for, or a clogged fuel filter will restrict the supply of fuel. However, plan on dropping off the car, and giving sufficient time for the mechanic to figure out the problem.

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What is the cost to resolve a P0171 code?

  • Estimated diagnostic cost: $100
  • Estimated part(s) + labor cost: $50–$800 (depending on diagnosis)
  • Estimated total cost: $150–$900

This code will require a diagnostic check, which will run about $100 depending on the time it takes to find the issue. As there is a laundry list of reasons why the engine runs lean, the average price per repair will vary greatly. You may get lucky with one of the simple repairs mentioned above. A broken vacuum hose sucking in air can be around $50, or a clogged fuel filter for $100. On the other hand, an oxygen sensor or mass air flow sensor can bring a bill of $400 to $500 dollars. A bad fuel pump can be really expensive costing around $600 to $800.

If you vehicle is throwing this code, schedule a diagnostic check with a mechanic immediately. Don’t have a regular mechanic? No problem. Use Openbay to compare pricing and schedule an appointment with quality mechanics in your area.

Service article written by an ASE Master Technician

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