Diagnostic Trouble Code P0172

P0172 “System Too Rich (Bank 1)”


What is code P0172?

Code P0172 stands for “System Too Rich (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 not getting enough air or are receiving too much fuel, leading to a “rich” 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 P0172 mean?

If code P0172 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 fuel (or not enough air), what is referred to as a “rich” operating condition, excess amounts of unburned fuel escape through the exhaust. Your engine loses fuel economy and emits more pollutants.

Code P0172 is the general code for a rich 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 (i.e. V6, V8, etc.) include two banks. In such cases, this code represents a problem on one side.

The ECM (engine control module) relies on a number of sensors to detect a rich operating condition, including the mass air flow sensor, manifold absolute pressure sensor (MAP sensor), and the oxygen sensors. If an engine is running rich, the ECM can make adjustments to compensate. If the problem is too far out of specification, however, a code P0172 will set and the check engine light will come on.


What causes code P0172?

A number of causes can trigger a code P0172. 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 P0172 include the following:

  • The check engine light is on or flashing
  • Reduced fuel economy due to excess fuel consumption
  • 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 P0172?

If a diagnostic scan of your vehicle indicates a code P0172, 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 clogged air filter, dirty mass air flow sensor, or leaking fuel pressure regulator. A temperature gun might also be used to monitor the temperature of the catalytic converter to determine if it is plugged.


How serious is this code?

You might not always notice a difference in how your vehicle runs with a code P0172, but it is not a good idea to drive for very long with this code present. A “rich” operating condition not only leads to a drop in fuel economy due to excessive fuel consumption, it can also cause increased engine emissions. More than that, if your engine is running “rich”, carbon buildup inside the combustion chambers is possible, as is an overheated and damaged catalytic converter. Code P0172 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)”

P0174 “System Too Lean (Bank 2)” 

P0175 “System Too Rich (Bank 2)”

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