The powertrain control module (PCM) controls the flow of fuel into the engine. It relies on several sensors to determine the most efficient amount to burn for power generation. One of these sensors is the air/fuel ratio sensor, which measures the oxygen level in the exhaust gases produced by the combustion process in the engine.
If the readings from the air/fuel ratio sensor shows that the fuel-air mixture is too lean during idle, the PCM will log a P2179 code.
The diagnostic trouble code (DTC) P2179 indicates “System Too Lean Off Idle Bank 2.” It applies to the bank of cylinders on the side of the engine without cylinder 1.
The air/fuel ratio sensor is actually an oxygen sensor that’s pulling double duty. Its readings guide the PCM when the controller adjusts various processes to achieve the most efficient engine operation.
A lean condition indicates the air-fuel ratio has too much air. When an engine runs lean, its performance suffers and its parts can develop serious problems. The PCM will try to correct the lean condition by either reducing the air intake, increasing the amount of fuel injected into the cylinders, or both.
The PCM regularly compares the amount of air and fuel that enter the engine. If the controller keeps seeing a lean condition in the bank 2 while the engine is idling, it will set the generic code P2179.
Note: The definition of code P2179 can differ according to the vehicle manufacturer. Check the appropriate repair manual or repair database for the exact code definition.
The P2179 code is a generic code that applies to various OBD-II-compliant vehicles. While it can show up in many makes and models, the cause and symptoms can vary between individual cases. Because of this, there is no single process to diagnose and fix the code.
If you’re not confident about conducting diagnostic tests on your vehicle, it’s a good idea to bring it to a professional mechanic. Otherwise, you can go ahead and diagnose the issue yourself.
Attempting to fix a P2179 code can become a challenging task if you don’t have the right tools and know-how to test your vehicle. In most cases, it’s best to leave the job to professionals.
For DIYers with advanced technical knowledge and hands-on experience who prefer to test and replace their vehicle’s faulty parts on their own, it will be helpful to rely on the appropriate repair manual or refer to an online repair database.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.