Will A P0420 Code Clear Itself?

P0420 catalytic converter

If you’ve ever seen the dreaded “check engine” light appear on your dashboard, you know it can be a cause for concern. One of the most common codes that trigger this warning light is the P0420 code. This code indicates a problem with your vehicle’s catalytic converter and can be a bit confusing for car owners who aren’t familiar with the ins and outs of engine diagnostics. One of the questions that many people have about this code is whether it will clear itself over time, or if it requires a professional fix. In this blog post, we’ll explore what the P0420 code means, what causes it, and whether or not it will clear itself.

What is the P0420 code?

The P0420 code is a generic diagnostic trouble code (DTC) that indicates a problem with your vehicle’s catalytic converter. Specifically, it indicates that the catalytic converter isn’t performing up to the standards set by your vehicle’s manufacturer. The catalytic converter is an important component of your car’s exhaust system that converts harmful pollutants into less harmful gases before they are released into the atmosphere.

What causes the P0420 code?

There are a number of potential causes for the P0420 code, including:

  1. Faulty catalytic converter: If your catalytic converter is damaged or worn out, it may not be able to convert pollutants as efficiently as it should. This can trigger the P0420 code.
  1. Oxygen sensor issues: Your vehicle’s oxygen sensors monitor the amount of oxygen in the exhaust system and send signals to the engine control module (ECM) to adjust fuel injection and ignition timing. If an oxygen sensor is faulty or isn’t reading correctly, it can cause the P0420 code.
  1. Exhaust leaks: Leaks in your exhaust system can cause an imbalance in the air-fuel ratio, which can trigger the P0420 code.
  1. Engine misfires: If your engine is misfiring, it can cause unburned fuel to enter the exhaust system, which can trigger the P0420 code.

Will the P0420 code clear itself?

Unfortunately, the P0420 code will not clear itself. This code indicates a serious problem with your vehicle’s emissions system that needs to be addressed in order to prevent further damage to your car and to the environment. While it’s possible for the check engine light to turn off on its own, this doesn’t mean that the problem has gone away. In fact, the code will likely return at some point, indicating that the underlying issue is still present.

How do you fix the P0420 code?

Fixing the P0420 code can be a complex process that often requires the help of a professional mechanic. The first step in addressing this issue is to diagnose the underlying problem that is causing the code to appear. This often involves a series of tests and inspections to determine if the issue is with the catalytic converter, oxygen sensors, or another component of the emissions system. Once the problem has been identified, the mechanic can take steps to repair or replace the faulty parts.

Some common fixes for the P0420 code include:

  1. Replace the Oxygen Sensor

One of the first steps to take when addressing the P0420 code is to replace the oxygen sensor. This can be done by purchasing a new sensor from your local auto parts store and installing it yourself or by taking your car to a mechanic.

  1. Fix Engine Misfires

If the P0420 code is caused by an engine misfire, it is important to fix the underlying issue before attempting to fix the code. This can involve replacing the spark plugs or ignition coils or cleaning the fuel injectors.

  1. Replace the Catalytic Converter

If the catalytic converter is the root cause of the P0420 code, it will need to be replaced. This can be done by taking your car to a mechanic or auto repair shop. The cost of the replacement will depend on the make and model of your car and the type of catalytic converter you need.

  1. Use a Catalytic Converter Cleaner

If the P0420 code is caused by a buildup of debris or other contaminants in the catalytic converter, you may be able to fix the issue by using a catalytic converter cleaner. These products are available at most auto parts stores and can be added directly to the fuel tank.

  1. Reset the Engine Control Module

Once you have fixed the underlying issue causing the P0420 code, you will need to reset the engine control module. This can be done using an OBD-II scanner or by disconnecting the battery.

  1. Repairing Exhaust Leaks

Exhaust leaks can also cause the P0420 code to appear. Leaks can occur anywhere in the exhaust system, including the manifold, pipes, and muffler.

If you suspect that an exhaust leak is causing the problem, you can try to locate it by listening for a hissing sound near the exhaust system or feeling for air escaping. Once the leak is located, it will need to be repaired by either welding or replacing the affected component.


In conclusion, the P0420 code can be caused by a variety of issues, including a faulty catalytic converter, oxygen sensors, or engine misfire. While there are a number of methods that can be used to fix the issue, it is important to first identify the underlying cause of the problem. This can be done using an OBD-II scanner or by taking your vehicle to a qualified mechanic or auto repair shop.

If you are experiencing the P0420 code, it is important to address the issue as soon as possible to prevent further damage to your vehicle’s engine and emissions system. With the right tools and knowledge, however, you can easily fix the problem and get back on the road in no time.

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