What Does the Engine Code P0420 Mean?

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If your car is showing the P0420 engine code, your catalytic converter is probably worn out or damaged. While this code doesn’t pose any danger to the driver, you should get it fixed promptly to avoid further problems such as a failed emissions test.   
Diagnostic trouble codes (DTCs) can help you identify a problem with your car’s engine. If you own an OBD-II code reader, it’s important to understand the meaning behind specific engine codes so that you can identify the source of car trouble, evaluate the problem, and find the right solution. 
Car insurance comparison and broker app Jerry can help you protect your car with expert information on DTCs and next-level savings on car insurance. In this article, we’re breaking down the P0420 engine code: what it means, how to deal with it, and how much it costs to fix. 

What does the engine code P0420 mean?

Definition: Catalyst system efficiency below threshold (Bank 1)
The P0420 engine code indicates a problem with your car’s catalytic converter, a key component in reducing emissions of toxic pollutants such as carbon monoxide, hydrocarbons, and nitrogen oxides. 

How much will it cost to fix?

If you need to replace the catalytic converter, the total cost of parts and labor could be $1000-$2500

What can cause the P0420 engine code?

If your car is showing the P0420 engine code, it’s likely that either the catalytic converter or the O2 sensors aren’t functioning properly. A faulty catalytic converter is the most common cause of this engine code. 
The catalytic converter is a small cylinder that lives in your car’s exhaust system. It uses a fine metallic honeycomb coated with platinum, rhodium, and other precious metals to convert toxic gases produced by the engine into safer emissions. Two oxygen sensors—positioned “upstream” and “downstream” of the catalytic converter—ensure that the filtration system is working. 
Other potential issues that could cause this engine code include: 
  • Leak in the exhaust system
  • Faulty oxygen sensor wiring 
  • High fuel pressure
  • Software in need of an update
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Common symptoms of the P0420 engine code

You may not see many symptoms accompanying this engine code other than the check engine light turning on. Other potential signs to watch for include: 
  • Sluggish acceleration
  • Decreased fuel economy 
  • Rotten egg smell from exhaust pipe 
  • A failed emissions test 
If your catalytic converter is actually clogged, you may also find that your car is frequently stalling or that it’s hard to start the engine

How serious is the P0420 engine code? 

Because the P0420 engine code typically doesn’t cause driveability issues, you might be tempted to overlook it. However, if you don’t deal with the issue promptly, it could cause further damage to other vehicle components
A P0420 engine code will also lead to a failed emissions inspection, so it’s a good idea to fix the problem if your state requires regular smog checks. 

Can I fix the P0420 engine code myself?

It may be possible to fix the P0420 engine code at home, but it’s important to diagnose the issue correctly before you begin any repairs. Depending on the source of the problem, you may need to: 
  • Replace the catalytic converter
  • Replace one or both of the O2 sensors
  • Replace the O2 sensor wiring or connectors 
You may also need to repair or replace the muffler, update your vehicle’s software, or replace any leaking components in the exhaust system. If you’re not sure what repairs your car needs, it’s a good idea to bring it to a professional for a thorough diagnostic inspection and repairs.

Replacing the catalytic converter

If you do decide to replace the catalytic converter yourself, you’ll need to follow these steps: 
  • Identify the correct part number. Make sure that you order a catalytic converter that will fit your vehicle. 
  • Disconnect your car’s battery before you begin any repairs. 
  • Remove the downstream and upstream O2 sensors. This is an optional step, but it can avoid accidental damage to the wiring. 
  • Unscrew the bolts to remove the old catalytic converter. If your catalytic converter is welded on, you may need to cut it out or take it to a mechanic. 
  • Install the new catalytic converter using a torque wrench. Be careful not to overtighten the bolts. 

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