P0420 Honda: Meaning, Causes, Symptoms & Fixes

So, you see that the check engine light is on the dashboard. You check things up with your repair sensor, and it states that you are dealing with the P0420 Honda issue. After researching a bit about the problem, you find that the issue is very common. 

Also, you see that many are stating that it is a severe problem and can cause damage. But is it actually that serious? And what is causing the problem to begin with? Well, this guide will cover all the things you would want to know regarding the issue. So, if you wanted to clear your confusion, you have come to the right place!

P0420 Honda

What Does P0420 Honda Check Engine Code Mean?

According to the definition, the P0420 states that the efficiency of the catalyst system is below the threshold. Now, the function of the catalytic converter is to break down the harmful pollutants that are created during the combustion cycle. It will then convert those pollutants into less harmful gasses. Same things happen when the P0420 is displayed in the dash of Ford.

That said, when you find the P0420 code in Honda, it indicates that the converter is not functioning efficiently. It would eventually result in the output of more harmful pollutants from your vehicle.

What Are The Symptoms of P0420 Code?

The symptoms of the P0420 code in Honda are pretty basic. And they are easily noticeable. Nonetheless, the symptoms that we are referring to are:

  • Check Engine Light will be on
  • The fuel economy will decrease
  • Lack of power from the engine
  • Sulfur or rotten egg smell

What Are The Causes of the P0420 Issue in Honda Accord?

As we have mentioned, the most common reason for the P0420 check engine code is a catalytic converter failure. But that does not mean that is the only reason why your check engine light is one. There are other potential reasons for this code. And if you really want to get to the bottom of the issue, you will need to know them all.

Nonetheless, the symptoms that are associated with the P0420 issue are:

  • Internally failing or worn catalytic converter
  • Faulty oxygen sensor (also a prime cause of Honda DTC P0134)
  • Faulty air-fuel sensor
  • A possible leak in the exhaust system
  • Misfire
  • Lean or Rich air-fuel ratio
  • Leaded gasoline

Among all of the reasons that we have stated, the catalytic converter is the most common. And the misfire, leaded gasoline, and lean or rich air-fuel ratio are the root cause of the converter failure.

P0420 in Honda Accord and Honda Civic

P0420 is a common error code that may appear in both the Honda Accord and the Honda Civic. This error indicates that there is a problem with the vehicle’s catalytic converter.

The exact causes of P0420 can vary depending on the specific model of Honda Accord or Civic, but they often involve problems within the catalytic converter itself or with other components in the vehicle’s exhaust system.

Fortunately, P0420 in Honda Accord and Civic vehicles can typically be fixed at a relatively low cost. So whether you’re driving a honda accord or a honda civic, if P0420 has struck your vehicle, you don’t need to worry – it can be sorted out with our following section.

How To Fix The P0420 in Honda?

How To Fix The P0420 Honda Issue

If you happen to have the P0420 Honda issue, do not worry. It is not the problem that will make you get a new ride. Instead, it is a common problem, and it has a fix. And to fix the issue, you will need to follow these steps:

Step 1: Diagnose the issue

Before anything else, you will need to get the issue diagnosed. And yes, it is certainly possible to diagnose the issue right at home. However, you might not have the knowledge or the equipment to work with your vehicle. In that case, going to your trusty mechanic would be the right choice.

Step 2: Get an accurate estimate for the repair

If you have diagnosed the problem in your home, you would want to go to a mechanic to get an estimate for the repairs. The last thing that you would want to do is waste your time and money on the wrong parts. And the good part about relying on reliable mechanics is that you will get a good warranty for the repair.

Step 3: Get the issue fixed

After getting the estimate, all that is left for you to do is to get the issue fixed. If you have opted for a reliable mechanic, the repair will go smoothly. And the cost for the repair will generally hover around the estimated range.

How To Diagnose the P0420 Civic Problem?

If you are aiming to fix the P0420 issue right at home, you will need to follow the proper steps. Aimlessly working with the problem will get you nowhere. And by the correct steps, we are referring to these:

Step 1: Use car repair sensors

First and foremost, you should use a car repair sensor to check if the P0420 is the only issue you are dealing with. If you find other codes or issues with your ride, you will need to get them addressed as soon as possible.

Step 2: Check the exhaust system

Next, you will have to pay close attention to the exhaust gaskets, pipes, manifold, and pre-catalytic converter. What you will be hunting for here are damages and leaks. If you find any leak, fix it and then clear the code. Then, finish a couple of drive cycles to verify whether the problem is still there or not.

Step 3: Check the O2 Sensor

When you get your vehicle running at an optimal condition, you should monitor the voltage reading from the downstream O2 sensor. For this, you can use a digital multimeter or car repair sensors. The sensor should output a relatively steady voltage. And it should read at about 0.45 V if the converter is functioning correctly.

However, if you notice that the reading is jumping from 0.1 volts to 0.9 volts, the catalyst is worn down. And you would need to get it replaced as soon as possible.

Is The Honda P0420 Issue Serious?

The issue severity of the P0420 is moderate. An extended driving session with this code going can cause internal engine damage. For this reason, you should get the issue fixed as soon as possible. That would allow you to prevent the engine and emission system damages.

What Is The Cost To Fix The P0420 Problem?

By now, it is clear that the P0420 issue can be for a bad sensor or a failed catalytic converter. The latter one is more serious, while the first one is less of an intensive repair. As multiple reasons can cause the issue, it is impossible to state an accurate estimate without getting the issue appropriately diagnosed.

If you take your vehicle to a repair shop, they will spend the first hour trying to get to the root of the issue. And the time that they will spend will add to the labor cost of the repair. Depending on the rate of the mechanic, this will generally cost you from $75 to $150.

On that note, most of the shops will add the diagnosis fee to any of the parts required for the repair. And depending on the cost of the parts, the shops will give you an accurate estimate for the entire repair.

Final Words

To recapitulate, the P0420 Honda is a common issue. The severity scale would reside in the moderate range in terms of the severity scale. And the most common cause of this issue is an internally failing or worn catalytic converter. 

Nonetheless, even though it is a moderate issue, you should not wait around. Instead, get the problem fixed as fast as you can! Also, if you want to learn about p0128, check our guide on P0128 code honda civic.