Openbay makes auto repair and service simple.

Compare estimates. Choose a shop. Schedule an appointment. Pay securely online.

How Openbay works

P0420 Diagnostic Trouble Code

Technical description

The catalytic converter has become less efficient at reducing pollution.

What P0420 really means?

The purpose of a catalytic converter is to lower the three main causes of pollution produced through gasoline combustion — carbon monoxide, nitrous oxide, and hydrocarbons (unburnt fuel). The toxic exhaust passes through a series of heated screens or honeycombs, which are coated with precious metals. These heated metals act as a catalyst that precipitates a chemical reaction, turning hydrocarbons into carbon dioxide and water, carbon monoxide into carbon dioxide, and nitrous oxide back into nitrogen and oxygen. Two oxygen sensors set into the exhaust before and after the catalytic converter provide the information to the computer about how well the catalytic converter is performing.

What are the causes of a P0420 code?

When the check engine light turns on for this code, you may be facing a big repair bill. Most catalytic converters fail because they are overworked. The primary reason is too much unburnt fuel is in the exhaust, either from a poorly running engine or too low a fuel octane rating for the car. Additionally, unresolved coolant or oil leaks that contaminate the combustion chamber can significantly shorten the life of a converter.

Get estimates for a P0420 diagnosis from nearby shops

What is the severity of a P0420 code?

Minor. Look to make an appointment when it is convenient to be without your car for a day.

What repair is typically needed to resolve a P0420 code?

Catalytic converter replacement. On most cars, unless the engine is running poorly when this code sets, the problem is emissions-related. The code must be addressed before any state emission test, but your car is not in danger of breaking down. Not much additional diagnosis is needed beyond ensuring that the oxygen sensors are working correctly (remember they police converter efficiency).

Catalytic converter replacement is often expensive. In some cases this repair can reach into the thousands of dollars range, and unquestionably, the type of car you drive will determine the price.

Openbay recommends that you replace your catalytic converter with an OEM part. This job may be in the $1200–$1500 range, possibly higher on exclusive models, but will fix the issue to factory specification.

For domestic-market vehicles, aftermarket or non-factory converters may be available, and will typically save you some money. These non-factory converters will work nearly as well as the original factory converter and can bring the price of the job down into the $500–$800 range. Generally, aftermarket converters won’t have the same amount of precious metal as the OEM part, so they aren’t as efficient — but they will keep the check engine light off. For foreign applications, the efficiency threshold is much tighter. Less expensive aftermarket converters are available, but the check engine light will usually return quickly.

Keep in mind, pricing will vary by location and your vehicle make and model. Save time and money by using Openbay to compare pricing and book an appointment with a service center in your area.

Service article written by an ASE Master Technician

Get estimates from nearby shops

How Openbay Works

  • Tell us about your auto service needs

    Openbay offers hundreds of maintenance, diagnostic, and repair services: from oil changes and brake jobs, to major suspension, electrical, and engine work. If you're not sure, describe the problem and we'll make recommendations.

  • Get estimates from nearby shops

    We get you detailed service estimates from our network of thousands of auto shops — usually within a few seconds. Compare on price, location, ratings, amenities, and more.

  • Book and pay securely online

    Once you choose a shop, book an appointment that fits your schedule. When service is complete, you authorize Openbay to make a contactless payment with your saved card.

  • Earn Openbay Rewards

    When you complete a service, you earn 1% of the invoice total as Openbay Rewards. They're instantly added to your account for use on your next service.

  • Manage your maintenance history

    When you create an account, your service history and upcoming appointments are always available online. Time to clean out the glove box!