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P0420 OBD-II Code

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OBD-II codes are diagnostic trouble codes that are used to identify issues with your vehicle.

These codes are stored in the engine control unit (ECU) and can be read using an OBD-II scanner.

An OBD-II scanner is a device that connects to your car’s onboard diagnostics system and reads the trouble codes from the ECU.

By reading these codes, you can quickly diagnose what is wrong with your car and take corrective action before more serious issues arise.

With an OBD-II scanner, you can save time and money by accurately pinpointing problems so they can be fixed right away.

A P0420 code is a generic OBD-II trouble code that indicates a malfunction in the catalyst system. Keep reading to learn all about this code and what you need to do if you come across it.

What is Code P0420?

P0420 is the generic OBD-II code indicating a malfunction in the catalyst system. This code is triggered when an oxygen sensor detects that the catalytic converter isn’t performing at its required efficiency level.

The catalytic converter is an important component in the exhaust system, as it converts toxic gasses from the engine into less harmful ones before releasing them out of the tailpipe.

A malfunctioning catalytic converter can lead to a range of issues including reduced fuel efficiency and increased emissions, so it’s important to identify and address the issue as soon as possible.

What are the Causes of Code P0420?

The most common causes of a P0420 code are: 

  • A faulty catalytic converter.
  • A damaged exhaust system (leaks or blockages).
  • An issue with the fuel system (such as an injector problem). 
  • An issue with the air intake system (such as a restricted air filter). 
  • A faulty oxygen sensor.
  • Clogged fuel injectors.


The most common symptoms of a P0420 code are: 

  • Loss of power and acceleration. 
  • Increased fuel consumption. 
  • Misfiring or backfiring engine.
  • Illuminated Check Engine Light. 
  • Rough idling or shaking
  • Increased emissions. 

If you come across a P0420 code, the best thing to do is take your car to a qualified mechanic as soon as possible.

A professional technician can use an OBD-II scanner to read the underlying codes and pinpoint the exact problem.

How to Diagnose and Repair Code P0420?

In order to diagnose and repair a P0420 code, you will need to use an OBD-II scanner to read the trouble codes stored in the ECU.

Once you have identified the issue, you can then begin to repair it.

Depending on the cause of the code, repair options could include replacing or repairing a damaged exhaust system component, cleaning clogged fuel injectors, or replacing an oxygen sensor.

It’s important to thoroughly inspect all parts of the system and make sure that everything is functioning properly before you attempt to start the engine again.

Cost to Fix

The cost to fix a P0420 code can vary depending on what issue is causing the code.

Generally speaking, repairs could range anywhere from $100 – $1,000, depending on the labor required and any parts that need to be replaced.

It’s important to get an accurate estimate before attempting any repairs to make sure you have a good idea of what the total cost will be.

Can You Drive with a P0420

Although you might not notice any significant issues while driving with a P0420, you’ll want to have the issue addressed right away.

Driving with an illuminated Check Engine Light can be dangerous, as it indicates that there is an issue with your vehicle which could cause more serious problems if left unchecked.

Not to mention, your fuel economy will automatically take a hit, meaning you’re not going to get the best gas mileage, which as we all know, can be painful to your wallet.