Diagnostic Trouble Code P0171

P0171 “System Too Lean (Bank 1)”


What is code P0171?

Code P0171 stands for “System Too Lean (Bank 1)”. This diagnostic trouble code can happen for a number of reasons related to combustion inside your engine. The cylinders in Bank 1 are receiving too much air or not enough fuel, leading to a “lean” operating environment. Therefore, it is important to have a qualified technician diagnose the specific problem that caused the code to be stored in your vehicle’s computer.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.

What does code P0171 mean?

If code P0171 shows up during a diagnostic scan of your vehicle, a technician knows that there is something going on with the engine intake, specifically the air and fuel mixture. Your engine requires a specific mixture of air and fuel inside the combustion chambers for combustion to happen properly. The ratio of air to fuel is also important to maximize engine performance, minimize emissions, and avoid engine damage.

If the air/fuel ratio is out of balance and the result is too much air (or not enough fuel), what is referred to as a “lean” operating condition, excess amounts of unburned oxygen escape through the exhaust system. Your engine loses fuel economy and emits more pollutants. A lean condition can also lead to significant internal engine component damage.

Code P0171 is the general code for a lean air/fuel condition in many engines. Bank 1 refers to the side of the engine that includes cylinder number 1. Many engines (such as four-cylinder models) only have one bank. Larger engines (V6, V8, etc.) include two banks. In such cases, this code represents a problem on one side.

If the ECM (engine control module) detects an issue with the air/fuel mixture, it will store a code P0171 and turn on the check engine light.


What causes code P0171?

A number of causes can trigger a code P0171. That is why an accurate diagnosis is essential. Causes of this code include:

Most likely

Other possibilities


What symptoms are associated with this code?

Common signs associated with a code P0171 include the following:

  • The check engine light is on or flashing
  • Reduced fuel economy
  • Failed emissions test
  • Engine shakes, runs roughly, or lacks power
  • Engine stalling or difficult to start
  • Engine sputters or hesitates on acceleration


How does a technician diagnose code P0171?

If a diagnostic scan of your vehicle indicates a code P0171, a technician will perform tests to pinpoint the problem. These tests include checking for any related trouble codes. The technician will also use the scan tool to read the live data of multiple values related to combustion that could directly affect how the engine runs. These include fuel pressure, injector pulse width, and mass air flow data. The technician might also inject additional fuel into the engine while it is running and observe oxygen sensor feedback data on the diagnostic scan tool. The fuel and intake system will also be visually inspected to look for common problems such as a damaged air filter, dirty mass air flow sensor, or leaking fuel pressure regulator.


How serious is this code?

You might not always notice a difference in how your vehicle runs with a code P0171, but it is not a good idea to drive for very long with this code present. A “lean” operating condition not only leads to a drop in fuel economy and higher emissions, it can also bring about much more serious problems such as spark knock, high exhaust gas temperatures, and internal engine damage.  Code P0171 is not a cause for immediate concern, but should be addressed as soon as reasonably possible.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.


Related Diagnostic Trouble Codes

P0170 “Fuel Trim (Bank 1)”

P0172 “System Too Rich (Bank 1)”

P0174 “System Too Lean (Bank 2)” 

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