Need car parts? Select your vehicle
Reading Time: 3 minutes
  • The diagnostic trouble code (DTC) P2179 indicates “System Too Lean Off Idle Bank 2.”
  • The powertrain control module (PCM) will log the P2179 code if it detects a lean condition in bank 2 while the engine is idling.
  • Common causes of the P2179 code are exhaust leaks, fuel delivery issues, and bad air/fuel ratio sensor or oxygen sensor.
  • A vehicle that sets the P2179 code can show symptoms like the check engine light switching on, insufficient engine power, and misfires.

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.

See also  P0138 Code: O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)

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.

What Does the P2179 Code Mean?

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.

image of an air fuel ratio sensor
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 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.

What are the Common Causes of the P2179 Code?

  • Exhaust leak
  • Fuel delivery issues
  • Intake air leak
  • Bad air/fuel ratio sensor or oxygen sensor
  • Bad mass airflow sensor
  • Internal engine problem
  • Circuit issues, such as a damaged wire or poor connection
  • Bad PCM or software in need of an update
See also  P0137 Code: Oxygen Sensor Circuit Low Voltage (Bank 1, Sensor 2)
checking a car fuel system hose
Exhaust or intake leaks can trigger the code P2179.

What are the Common Symptoms of the P2179 Code?

How to Diagnose the P2179 Code

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.

How to Fix the P2179 Code

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.

About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Contact Center Manager and Technical Reviewer at

William “Bill” Guzenski has produced hundreds of how-to videos for the automotive community. He’s an ASE Certified Master Automobile Technician, and is affiliated with the Specialty Equipment Market Association (SEMA). He loves attending race events and car shows throughout the country, as well as traveling in his 40-foot motorhome, exploring abandoned mines and ghost towns.

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.

File Under : OBD-II Trouble Codes Tagged With :
carparts answers
Notify of
Inline Feedbacks
View all comments

View all Questions & Answers

In the garage logo Newsletter Answers BE PART OF OUR COMMUNITY: Share your knowledge & help fellow drivers Join Now
Copyright ©2023, Inc. All Rights Reserved.