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  • The P0431 code stands for “Warm Up Catalytic Converter, Bank 2—Efficiency Below Threshold.” It’s triggered when the PCM detects that the catalytic converter is not efficient enough based on factory specifications.
  • Some possible triggers for the code include a bad catalytic converter, a faulty oxygen sensor, and an exhaust leak.
  • Symptoms to look out for are diminished fuel efficiency and decreased engine performance.

The P0431 code indicates the powertrain control module (PCM) has perceived the warm up catalytic converter (on bank 2) is not operating properly. If your vehicle logs this code, it is important that you familiarize yourself with what it entails before troubleshooting. What does the engine code P0431 code mean, what are its possible causes, and how is it fixed? Read on to learn the answers to these questions and mode.

catalytic converter 6
The PCM will store code P0431 if it reads that the upstream and downstream oxygen sensors of the catalytic converter on Bank 2 are reflecting similar exhaust oxygen concentration.

What Does the P0431 Code Mean?

Diagnostic trouble code (DTC) P0431 stands for “Warm Up Catalytic Converter, Bank 2—Efficiency Below Threshold.” It means that your car’s primary computer or powertrain control module has detected that the catalytic converter is not efficient enough based on factory specification. The downstream sensor is the one between the two catalytic converters in the illustration shown.

See also  P0136 Code: O2 Sensor Circuit (Bank 1, Sensor 2)
oxygen sensor diagram
Oxygen sensor diagram | Image source: Richard McCuistian

Catalytic converter efficiency is monitored using upstream and downstream oxygen sensors. Most of these sensors contain zirconium dioxide-sensing elements enclosed by vented steel housings. These are connected to the lead wires in the oxygen sensor wiring harnesses via platinum or gold plated connector terminals.

o2 sensor reading
Notice that the /2 sensors are much less active than the /1 sensors, which is proper. | Image source: Richard McCuistian

The PCM will store code P0431 if it reads that the upstream and downstream oxygen sensors of the catalytic converter on Bank 2 are switching near the same rather than the rear sensor reflecting a lazy signal, as is normal (see illustration). This code will also activate the malfunction indicator lamp.

jeep 02 sensor reading
This is what the O2 trace looks like when the catalyst isn’t storing oxygen at all. This is a Jeep that came in with gutted catalytic converters. | Image source: Richard McCuistian

Read our technical discussion about how the catalytic converter works to pick up more information that can help you resolve code P0431 if you’re looking for a DIY fix.

Note: The definition of code P0431 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Possible Causes of the P0431 Code?

Here are the common causes of the P0431 code:

See also  P0174 Code: System Too Lean (Cylinder Bank 2)

What are the Common Symptoms of the P0431 Code?

Depending on the severity of the catalytic converter problem, other related DTCs may also be stored. Their symptoms may vary or overlap. Regardless of whether you’re dealing with multiple DTCs or just the P0431 code, you can expect an illuminated check engine light. Here are other symptoms you may experience with the code P0431:

  • Diminished fuel efficiency
  • Decreased engine performance
check engine light is on 1 5
An illuminated check engine light is a common symptom of error code P0431.

How to Diagnose the P0431 Code

Diagnosing code P0431 can get a little tricky as the process may vary depending on the year, make, and model of your car. For example, diagnosing a P0431 in a Mitsubishi may involve steps that are different from what the owners of other makes and models follow. The viable solution would be to seek a certified mechanic’s help to save yourself from costly mistakes.

How to Fix the P0431 Code

There’s no universal fix to clear the P0431 code as the solution varies based on the causes and the vehicle’s make and model. If you’re not confident with your DIY skills and knowledge about the code, it is best to let the professionals handle the job.

See also  How Long Does a Catalytic Converter Last?

If you have decent DIY skills to work on your car, you may use online auto repair resources and guides to figure out the proper way of fixing DTC P0431. One of the best examples you could use is ALLDATA. This subscription will give you access to thousands of information that you can use for your convenience. Also, keep in mind to cross-check with the repair manual before starting the repair process.

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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 Technical Reviewer at

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.

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Steve Robinson

Excellent description. Great informational article.

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