How to Fix P0420 Engine Code?

One of the most common problems with your car is its exhaust or fuel systems. Using the Vehicle PCM computer, yoVehicleet the P0420 engine code.

What is the P0420 Engine Code?

The P0420 Engine Code means that the Vehicle’s computer (PCM) has a problem with the low catalyst converter system efficiency. It also means that oxygen levels are below the desired threshold, which can result in problems with a car’s exhaust or fuel systems.

If your Vehicle’s PCM throws a PVehicle’s code, the catalytic converter system efficiency is below the desired threshold. This can be caused by several problems in your car’s exhaust or fuel systems, so it’s essential to identify and address the underlying issue as soon as possible. Fortunately, there are several methods you can use to fix this problem and get your car back on track.

P0420 engine code in PCM car computer

How to Fix P0420 Engine Code?

  • Check the exhaust system: Look for any physical damage to the catalytic converter or other parts of the exhaust system that might be causing the problem.
  • Verify the code: Using an OBD-II scanner, check to ensure that the P0420 code is the only one stored.
  • Check the O2 sensors: Inspect the oxygen sensors for damage or contamination. They play a crucial role in determining the efficiency of the catalytic converter.
  • Check the fuel system: Make sure the fuel system is operating correctly, as a lean fuel mixture can cause the catalytic converter to work less efficiently.
  • Check engine misfires: If the engine is misfiring, it can cause the catalytic converter to work less efficiently.
  • Check for vacuum leaks: Vacuum leaks can cause the engine to run lean, leading to a P0420 code.
  • Replace the catalytic converter: If the above steps don’t solve the issue, it may be necessary to replace it.


The first step in solving this issue is diagnosing the root cause of your P0420 code. This could be anything from an oxygen sensor malfunction to an exhaust leak or, even more severe, a faulty catalytic converter. If you suspect that any of these issues may be causing your P0420 engine code, it’s essential to have them checked out right away by a qualified mechanic or technician.

Once you’ve identified and addressed the underlying issue, there are some basic maintenance tasks you should regularly perform to keep your car running smoothly and avoid similar problems in the future. For example, it is recommended that you check and replace your oxygen sensors regularly, as they play a crucial role in monitoring catalytic converter performance. You should also inspect your exhaust system for leaks periodically, as even small cracks can allow unburned fuel into the system, leading to decreased efficiency and throw-off engine readings. Additionally, ensure all your spark plugs are in good working order, as faulty plugs can contribute to poor catalytic converter performance.

Finally, if all else fails and you’re still having trouble with your P0420 engine code after performing some basic maintenance tasks, it may be time for a new catalytic converter. While replacing this component is not cheap, it will dramatically improve your engine’s performance if done correctly. Be sure to consult a trained technician before making significant repairs or replacements, though!

Overall, diagnosing and fixing a P0420 engine code requires some knowledge of automotive repair and regular maintenance tasks. Still, with patience and perseverance, you’ll have no trouble getting back on track quickly and safely!

You can read our detailed article about the 7E8 engine code.


Robert Aksamit

Robert Aksamit

Robert Aksamit is a mechanical engineer and automotive industry expert. Robert was born in Minnesota and worked in the US automotive industry for 25 years. He is highly regarded for his passion and dedication to continually improving vehicles in response to customer feedback. Robert has a keen eye for sourcing the best vehicle components and materials on the market and is always looking for ways to enhance the user experience. As a writer, Robert covers automotive-related topics. Read more on Robert Aksamit's about page. Contact Robert:

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