What Does p0420 Code Honda Civic Mean?

By Nick Marchenko, PhD

For a start, if you are getting the p0420 Honda code, it probably means you are having a bad catalytic converter. The vehicle's PCM usually detects this code, a sure-short pointer to a malfunctioning catalytic converter. 

You need to know that catalytic converters are responsible for removing harmful pollutants from exhaust pipes. They do this by reducing the amount of contaminants that are produced during the combustion process. If your vehicle detects po420, it does not mean the driver is in some danger, but still, it's important to get it fixed as soon as possible. 

What Does the p0420 Code Mean for Honda Civic?

First, let's talk about the code and what it stands for. P0420 stands for catalytic system efficiency below threshold. 

In the context of the Honda Civic, this is a generic OBD || trouble code that highlights the malfunction in the catalytic converter of the Honda Civic.

In the Honda Civic, your catalytic converter reduces harmful emissions because it converts the toxic gasses into less harmful ones. By any means, if it is not functioning properly, then you will get the code.

Description of the Code 

• P means PowerTrain, and it's related to Engine and Transmission.
• 0 is Generic
• 4 is related to emission control.
• 20 implies a problem with catalytic converter efficiency.

Possible Causes for p0420 Code for Honda Civic 

Now is the time to examine the possible causes or factors that trigger p0420 for the Honda Civic.

Catalytic converter failure issue

We already know that the catalytic converter failure issue is the most common cause of p0420. The dilemma with a catalytic converter is that it can deteriorate or clog over time, eventually reducing its efficiency. 

Issues with Oxygen Sensors

You will find oxygen sensors in your Honda Civic's upstream and downstream areas. They monitor the exhaust gasses and the catalytic converters' efficiency. Let's say that one of the sensors is not working properly. This can also lead to the trigger of po420.

Exhaust System Leaks

Sometimes, leaks in the exhaust system can introduce false oxygen sensor reading, which eventually triggers the code.

Issue with MAF sensors 

MAF stands for mass air flow sensors and measures engine air entering. If there is some issue with this sensor, there can be a bigger problem with the fuel and air ratio that can affect the catalytic converter's efficiency. 

PCM/ECU Software Issues 

It is not common, but sometimes, the code can also be triggered if there is any issue with programming or software within the PCM module or engine control unit.

Common Symptoms of Honda Civic P0420 Trouble Code

• The first symptom of Honda Civic p0420 is the elimination of the check engine light on the dashboard. The light shows some issues with the car diagnostic system.
• Naturally, when the code is triggered, you will see the malfunctioning in the catalytic converter, which will eventually lead to decreased fuel efficiency. 
• You may also see a decrease in the responsiveness of the engine because it will not perform well.
• Sometimes, the engine may halt or come to a stall because the code will trigger problems in the air/ fuel mixtures. 
• Your vehicle will likely fail an emission test if the catalytic converter is not performing well. 
• There is also the possibility that you hear the rattling noises. 

How Do I Fix Honda Civic p0420

Technically, if there is an issue with the catalytic system of the vehicle, then it will not perform well and get into a lot of trouble with time. It is imperative to think about the fixes when the code is triggered. Let's take a look at what you can do. 

Replace the Catalytic Converter

What do we do when we sense something faulty in our machinery? Our first option is to replace it, which is the case with a catalytic converter. 

If your Honda Civic shows the p0420 code, you need to replace the catalytic converter. You will find original equipment manufacturer options, but it is important to ensure that the replacement meets your Honda Civic's emission standards.

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Repair Exhaust System Leaks

Sometimes, there is an issue in the exhaust system that is triggering the code. If so, you must replace or fix the gasket components or pipes to make everything right.

Fix Fuel System

Sometimes, you must look for fuel injector issues or pressure regulator issues. Make sure you maintain the correct air-fuel mixture to handle the problem.

How Much Does It Cost to Fix P0420?

There is no fixed cost for p0420. But on average, replacing the faulty catalytic converter can cost you between $500 to $1500. 

Replacing the oxygen sensor can cost you between $150 to $300, and the diagnostic cost varies.

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Can I Drive a Honda Civic with the PO420 code?

If you really have to drive your Honda Civic, then you can keep driving even when there is a diagnosis of po420 code, but it is not recommended for a long time. 

FAQs

How often should I replace the oxygen sensors?

Oxygen sensors usually can last for 60000 to 100000 miles, but getting them checked often is important to have an idea.

How will I know if I have an issue with my exhaust leak after I get the code?

There are different symptoms for that. For instance, you will hear the rattling noises and smell strong fumes.

Can I install the aftermarket catalytic converter?

Yes, there is a possibility, but make sure that the aftermarket catalytic converter matches the emission standard of your Honda Civic. 

Nick Marchenko, PhD

Industrial Engineer & Automotive Content Specialist

Nick writes in-depth guides on car clubs, engine specs, vehicle ownership, and modifications, combining engineering knowledge with automotive passion.

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