What is P0172?
Error code P0172 is an OBD-II diagnostic trouble code (DTC) defined as “System Too Rich (Bank 1).”
The P0172 error code is set when your Engine Control Module (ECM) or Powertrain Control Module (PCM) detects that there’s too much gasoline present in the air fuel mixture of your combustion chamber.
If you want to maintain maximum engine power and fuel efficiency, your air fuel ratio should be about 14.7:1. This air fuel ratio has the highest power output but the best fuel economy.
Your Engine Control Module and Powertrain Control Module have the ability to adjust your air fuel ratio through your oxygen sensors, air fuel sensor (AF sensor), and Manifold Absolute Pressure sensor (MAP sensor). However, they can only do so in small increments.
So, if your air fuel ratio requires greater adjusting than normal, error code P0172 will be set.