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Summary
  • Diagnostic trouble code (DTC) P0173 stands for “Fuel Trim Bank 2.” This code indicates that your car’s fuel trims have reached their operational limitations (maximum rich or maximum lean).
  • The code is logged once the fuel trim mixture has become abnormally lean. On some vehicles, it can mean that there’s an overly rich mixture.
  • Air vacuum leaks, exhaust leaks, bad O2 sensors, malfunctioning mass air flow sensors, circuit issues, and fuel delivery problems can cause a P0173 code.
  • The common symptoms of this error code include hesitation during acceleration, poor fuel economy, and intermittent stalling.

Air-fuel ratio is important to ensure excellent engine performance. Your powertrain control module (PCM) plays an important role in maintaining this ratio. If your PCM is unable to adjust your vehicle’s air-fuel ratio due to vehicle problems, it may trigger fuel-trim related trouble codes, such as code P0173.

If you encounter a P0173 code, here’s what you need to know about it:

car fuel
The P0173 code indicates that your car’s fuel trims have reached their operational limitations

What Does the P0173 Code Mean?

Diagnostic trouble code (DTC) P0173 stands for “Fuel Trim Bank 2.” This code indicates that your car’s fuel trims have reached their operational limitations (maximum rich or maximum lean). Fuel trim is the ongoing adaptation that the PCM makes to the fuel mixture to maintain a balanced air-fuel ratio. Usually, code P0173 means the fuel trim mixture has become abnormally lean (too much air; not enough fuel), but it can also point to an overly rich mixture (too much fuel; not enough air) on some cars. We recommend that you avoid driving once your vehicle’s triggered a P0173 code.

You can learn more about fuel trim in our in-depth technical discussion about long-term and short-term fuel trim and how to use a scan tool to diagnose P0173 and similar codes.

What are the Possible Causes of the P0173 Code?

Here are the most common causes of a P0173 code:

  • Air (vacuum) leaks or exhaust leaks
  • A faulty sensor  (e.g., oxygen sensor or mass air flow sensor)
  • Circuit issues, such as a damaged wire or poor connection
  • A fuel delivery problem (e.g, faulty pump or clogged injector)
mechanic checking fuel injector
A clogged injector can trigger the P0173 code.

What are the Common Symptoms of the P0173 Code?

Here are some common symptoms of a P0173 code:

How to Diagnose the P0173 Code

Trouble codes can be too technical to diagnose on your own. If a P0173 code shows up after you use a scan tool, it’s best to ask a mechanic for help. However, you can also try checking out online resources to get a better understanding of this trouble code. Watch these videos to learn more about diagnosing a P0173 code:

How to Fix a P0173 Code 

Dealing with trouble codes can sometimes be too difficult for a DIYer. Professionals undergo extensive training to learn how to efficiently fix vehicle problems that trigger trouble codes. Consulting a mechanic can be the best way to fix vehicle issues that have triggered a P0173 code.
You can also try to learn about diagnosing and troubleshooting OBD codes. Research about the underlying complications linked to the P0173 code. You can then try to determine what’s triggering the code and decide what to do. You can also check technical service bulletins (TSBs) or recalls that may be related to the P0173 code if you have access to a repair manual or repair database. Depending on its make and model, some fixes may not work for your vehicle. What resolves the issues triggering a P0173 in a BMW may not work for a Mercedes Benz. If troubleshooting a DTC becomes too difficult for you, don’t hesitate to ask a mechanic for help.

Where to Find Replacement Parts to Fix Code P0173

It’s best to clear code P0173 immediately to avoid costly repairs down the line. After all, it indicates issues in crucial parts, like the oxygen sensor and mass airflow sensor. Thankfully, getting a replacement is easy with CarParts.com.

Simply use your mobile phone or computer to check out our catalog. Enter your ride’s year, make, and model into our vehicle selector to view compatible products. If you’re shopping on a tight budget or have a go-to brand, you can view the parts that fit your needs using the filters.

On hand and ready to ship, our replacement parts are available at competitive prices. We ship them from strategically located warehouses across the US, so you can expect your order in as fast as two business days.

Don’t wait for other trouble codes to get logged alongside the P0173 code. Address the issue immediately with the appropriate part replacement from CarParts.com.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com 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 CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

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
Garage Essentials
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