Error Code P0432 is defined as Main Catalyst Efficiency Below Threshold, Bank 2. This code indicates that the efficiency of the emission of Bank 2 Main Catalytic Converter, has fallen below its minimum allowable limit.

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


The catalytic converter (catalyst) in vehicles works by improving the tailpipe emission, oxygenating the exhaust gasses. It converts HC (hydrocarbons), CO (carbon monoxide) and NOx (nitrogen oxide) into H2O (water vapor), CO2 (carbon monoxide) and N (nitrogen).

The PCM (powertrain control module, also known as ECM or engine control module in other makes) monitors the efficiency of the catalyst through the post-catalyst O2 (oxygen) sensor. This sensor functions primarily for this purpose. It works by switching much more slowly than the front O2 sensor. If at any point, the PCM detects the post-catalyst O2 sensor is switching too fast (which indicates no change between the inlet and outlet of the catalytic converter), it will interpret this as a malfunction, and trigger the Error Code P0432.

The Catalyst Monitoring O2 sensor, which is found near the outlet of the Catalytic Converter, is the one that tracks the threshold for the emission efficiency.

Bank 2 simply refers to the side of the engine that does NOT contain cylinder #1.

Common Symptoms

As with other error codes, this code triggers the Check Engine light. Other than that, there aren’t many symptoms for this error code, aside from increased tailpipe emissions.

Possible Causes

There are a couple of main factors for this error code to show up, which are:

  • Engine running at outside its optimal air:fuel ratio
  • Damaged or non-functional catalytic converter
  • Engine misfires causing damage to the catalyst
  • Internal engine damage that causes the engine to have high oil consumption
  • Head gasket leak which caused damage to the catalytic converter

How to Check

Catalytic converters contain precious metals, such as palladium, platinum and rhodium. Cheaper catalytic converter has less of these precious metals. Thus, it is important to note that some vehicle makes are quite finicky when it comes to the catalytic converter, and how the PCM works to monitor the. So just because the parts guy in the automobile accessories and parts store says it will work, doesn’t mean that it will. The reason behind this is the engineering behind the vehicle; those vehicles made with the highest quality of metals in their catalytic converter will definitely need the replacement of the catalytic converter with the same quality, and low cost catalyst will not work for them.

Also, there are many different kinds of catalysts. Some makes actually allow the use of cheaper catalyst, while others will not. Toyota and Subaru for example, are known for this. Subaru will require CARB certified catalysts to keep its Check Engine light off, and will never tolerate aftermarket catalyst, no matter how expensive it can be.

How to Fix

If you’re having this code, it is either the catalytic converter is the problem, or the engine ran out of optimal air:fuel ratio. A tune up or engine repair may fix this problem. Otherwise, you may need to replace your catalytic converter.

Some of the most common misdiagnosis of this error code are:

  • Replacing the catalyst, when it is the misfiring engine that is causing the problem
  • Replacing the catalyst, when the problem is caused by internal engine damage, which makes elevated emission levels
  • Replacing the O2 sensor when the problem is the damaged catalyst