Error Code P0431 is defined as Warm Up Catalyst Efficiency Below Threshold (Bank 2). This code refers to a failure in the catalytic converter caused by either too much or too little fuel intake, or contamination from engine oil.

This error code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II, particularly vehicles made since 1996 up to present. Specifications on the definition, troubleshooting and repairs of course, vary from one make and/or model to another.


Error Code P0431 indicates that the PCM (powertrain control module, also known as ECM or engine control module), has detected a problem on the efficiency level relating to the engine’s warm-up catalyst. Vehicle manufacturer provide the standard specifications for the warm up. In some cases, this problem can be a symptom of general failure of the catalytic converter. The PCM works by monitoring the intake of oxygen into the catalytic converter. Should there be a discrepancy between the manufacturer’s reference and the intake, then it will set the trouble code.

This code basically means the O2 (oxygen) sensor downstream of the catalytic converter on bank 2, has determined that the converter is not working as efficiently as it should be, based on the specifications. The

Common Symptoms

Symptoms for Error Code P0431 usually depend on the root cause of the problem. If the problem is caused by lowered efficiency of the catalytic converter, there are usually no noticeable issues while driving the vehicle. If the problem however, is caused by significant damage or malfunction in the catalytic converter, then it can most definitely impede, or even disable the vehicle’s engine.

Other common symptoms for this error code include rough or hard idle when engine is cold.

Possible Causes

There are many factors that lead to this error code. Some of the most possible causes are:

  • Malfunctioning catalytic converter
  • Defective (no reading properly) O2 sensor
  • Exhaust leak

How to Check

Mechanics diagnose this error code by conducting a thorough inspection of all the electrical connectors related to the catalytic converter. They will look for faults or corrosion.

Also, they counter check any electrical findings the PCM have gathered from the catalytic converter with the manufacturer’s reference to gauge the severity of the problem.

How to Fix

Repairs for this code are pretty easy and straightforward, which of course, can be derived from a thorough diagnosis of the problem. Some of the most commons fixes are:

  • Repair or replacement of broken or faulty parts connected to the catalytic converter
  • Damaged catalytic converter must be replaced with a new one
  • Vehicle should be retested after each individual repair to properly pinpoint the cause of the problem

The severity and seriousness of this error code vary, depending on the cause of the problem. In the worst cases, this code can completely disable the cause of the engine damage. And if left unchecked, the damaged components may cause further strain on the parts related to the converter. Thus, it is important to address Error Code P0431 as soon as possible.