P0420 Toyota Camry – Definition, Causes, Symptoms

P0420 Toyota Camry – Definition, Causes, Symptoms

August 26, 2022 0 By CarGuy

Have you gotten the check engine light and you diagnosed the P0420 Toyota Camry code? Well, if that is the case, then you are at the right place because there will be a lot to cover on this topic where we are going to learn everything when it comes to this specific problem that you are dealing with.

Doing a proper research on a problem is always a good thing. Research is key to any aspect of life. Starting from buying a car, to solving problems, everything requires good research skills. But not only that, but you also have to step up your troubleshooting skills.

Especially when it comes to modern vehicles that have a ton of sensors on them. Modern cars tend to have a ton more problems than cars back in the day. And modern problems require a more modern approach. This means that you need to have the proper tools and also you need to follow proper procedures to get things done the right way. But you shouldn’t worry because we are going to help you out.

First, we are going to learn what is modern car diagnostics and how it’s done the right way. Then we will cover the P0420 Toyota Camry code and learn more about its definition. Then we will learn how catalytic converter works and after that, we will cover all the possible causes of this issue and how to diagnose it the right way. So, if you want to learn more about solving this problem, follow along.

Introduction To Car Diagnostics

Now before we dive into the P0420 Toyota Camry and learn more about the problem itself, let’s first introduce ourselves to the topic and learn more about car diagnostics in general.

As you probably know, modern car diagnostics is not like car diagnostics back in the day. Back in the day things were easy and mechanics often relied on their experience to diagnose problems in cars.

But modern cars require a more modern approach. And diagnosing a car based on the symptoms could help you but in most cases, it will not solve your problem. You will end up guessing and replacing a ton of parts on the car before you solve the issue, costing you hundreds of dollars. And this is something that you want to avoid.

So, what is this modern approach? Well, the modern approach when it comes to dealing with these issues requires using advanced tools that will help you to gain an access to the car computer. And this tool is known as the OBD2 scanner.

The OBD2 scanner will scan the PCM and will list all of the problems that your car has and you will be able to start sorting the issue. But, there is also another tool that you will need, especially when we are dealing with sensors.

And this tool is the multimeter. Having a multimeter is key when it comes to tackling sensor-related problems. With this tool, you will be able to measure the performance of this specific component and deem if it’s good or not. And replace it if necessary. That’s why you should have both of these tools.

But what about the P0420 Toyota Camry? Well, more on that we are going to elaborate on in the following chapter.

P0420 Toyota Camry Meaning – Catalyst System Efficiency Below Threshold (Bank 1)

Now let’s move on and start discussing about the P0420 Toyota Camry meaning. What this code means and what could be the problem with your Camry?

Well, the simple definition for the P0420 code is “Catalyst System Efficiency Below Threshold (Bank 1)”. So, what does this means in the first place? Should you be worried?

Well, you should be worried because this code indicates that the catalytic converter on bank 1 of your engine does not perform well.

If you didn’t know, bank 1 refers to the bank where cylinder number 1 is located. So, this should be your first clue where to look for in order to solve this problem, the catalytic converter on the bank 1 side. But does this really mean that the catalytic converter is done and you have to replace it?

Well, not quite. This code can be also triggered by problems with other components as well. So, you shouldn’t alarm yourself too much concerning this issue at this point. First, thing first you need to learn what is a catalytic converter, and more on this we are going to cover in the following chapter, where we are going to explain everything about this component. So, follow along if you want to tackle the P0420 Toyota Camry code.

What Is A Catalytic Converter?

Now let’s take a peek into what is a catalytic converter. Why is this important? Well, as we noted previously, the work of this component is the primary cause for the P0420 Toyota Camry. So, we think that we need to learn more about this component and understand how it works. So, let’s get into it.

If you didn’t know, catalytic converters are emissions devices that are installed on vehicles with internal combustion engines.

These catalytic converters became the norm because back in the day cities were full of smog and other heavy pollutants from the traffic. And something had to be done, so the catalytic converter was invented because of this problem.

This is a component that resembles a small muffler from the outside and is mounted right after the exhaust manifold. On both ends, there are O2 sensors that are mounted.

Inside the catalytic converter, there is a honeycomb structure through which the gases flow and convert into something less toxic.

And what can happen is that this converter can get clogged up over time and cause problems. Like in our case with the P0420 Toyota Camry.

Many different conditions can cause the catalytic converter to fail and this is why we are going to further discuss them in the following chapters in detail. So, you don’t want to miss that.

What is important for you as a car owner is that this catalytic converter once deemed not worthy, has to be replaced if you want to resume driving the car properly. Later on, we are going to discuss more about this. Now let’s cover the causes of the P0420 code.

P0420 Toyota Camry Causes

So, we learned a bit about the definition of the P0420 Toyota Camry code, now let’s take a look at the causes for this code.

As you probably know, everything happens for a cause and so is the case with this P0420 code. This is why we are going to cover all the possibilities in-depth and see where you should look for the solution to your problem.

1. Faulty Catalytic Converter

The first and most common cause for the P0420 Toyota Prius is probably the faulty catalytic converter.

The code is self-describing. In most cases, the catalytic converter on bank 1 of your engine has failed.

It is either clogged up and is restricting. Or the honeycomb structure inside of the catalytic converter is disintegrated. Once these two situations occur, you will be notified with the check engine light and the trouble code P0420 Toyota Highlander. But this doesn’t mean that there could not be other reasons.

P0420 Toyota Camry

So, if you really doubt that the catalytic converter is the real problem, you might want to check out the rest of the causes that we are going to list next.

2. Bad O2 Sensor

The next very common reason that we are going to discuss for the P0420 Chevy code is the bad O2 sensor.

As you probably know, O2 sensors are the ones in charge of measuring the flow of oxygen inside the exhaust pipe.

In each car, you have at least two of them. One is the upstream sensor located before the catalytic converter and the second is the downstream sensor located after the catalytic converter.

Sometimes these sensors can break and potentially damage the work of the catalytic converter. Especially if it’s the first sensor. And what can happen is that you can get wrong readings and also problems like in this case with the check engine light and the P0420 Ford code. Now let’s move on to the next probable cause.

3. Exhaust Leaks

The next probable cause for the P0420 Toyota Camry code is connected to exhaust leaks. But what is an exhaust leak?

Well, an exhaust leak in simple terms is a leak of exhaust gases that are found somewhere from the engine to the rear end of the vehicle.

But the most problematic are the leaks before the catalytic converter. These are leaks caused either by a bad exhaust manifold that is cracked. Or possibly by broken exhaust manifold bolts. The second cause is rather a common thing on cars.

So, if you are experiencing something like hissing coming from the front end of the vehicle, then you definitely need to check it out and sort out the problem accordingly.

A thorough inspection will tell quite a lot about potential problems such as these. This is why you should not be afraid to turn on your flashlight and see if there are dark spots caused by exhaust fumes. Now let’s move on to the next probable cause for the P0420 Toyota Camry code.

4. Rich Air To Fuel Mixture

Now let’s cover some odd causes that could cause a problem like this with the P0420 Toyota Camry. And these are probably things that you never presumed existed.

The first cause that we are going to cover is the rich air-to-fuel mixture. So, what is the situation when your car is running rich?

Well, this is the situation when you have a car that is wasting more fuel than air. This means that it runs really reach and is far behind the optimum engine performance. And frankly, this is something that you don’t want.

Running rich at start-up is normal but after the engine warms up, the A/F ratio should smoothen up. So, when you have this situation in your engine, damage to the catalytic converter is unavoidable. The catalytic converter will get clogged up eventually and you will get a check engine light with the P0420 code, or P0430 if it’s the other bank.

5. Lean Air To Fuel Mixture

The second cause for this situation with the P0420 Toyota 4Runner is the lean air-to-fuel mixture. So, what is a lean A/F mixture?

Well, this is completely the opposite of a rich air-to-fuel mixture. When a car runs lean it means that there is a problem with the A/F again.

So, this could also affect components like the spark plugs and catalytic converter. So, you definitely need to check this cause as well. Even though the rich air-to-fuel mixture is much more dangerous I must admit. Now let’s move on to the last cause for the P0420 Toyota Camry code.

6. Oil Burning Engine

And the last cause for the P0420 Toyota Camry code that we are going to cover is the situation when the engine is burning a lot of oil.

Especially if you have an old engine that has seen better days. The more oil the engine burns, the bigger the chance to clog up the catalytic converter and cause a check engine light and a code like in this situation.

When it comes to this issue, sadly, you cannot do much except replace the engine or fix the engine head if they are causing the issue and have some burnt valves.

If the problem is caused by the piston rings, then you will have to do a bigger engine overhaul or replace this engine with a used engine to solve this problem the right way. Now let’s move on to the symptoms that you are going to experience when you are having a P0420 Toyota Prius code.

P0420 Toyota Camry Symptoms

Now let’s dive into the P0420 Toyota Camry symptoms. As you probably know, there are also symptoms when you experience a problem like in our case with this trouble code. So, what are the symptoms?

Well, the most common one is probably the check engine light. And since you are already here, you are aware of this symptom. What is interesting is that in most cases, whenever you have a code like this, you will also get other codes as well.

So, we can say that the problem is a consequence of other situations. Like engine misfires, lean or rich air to fuel mixture and oil burning problems. These things all affect the engine catalytic converter and this is why you should fix these things first before you try to solve the P0420 code.

What are the other symptoms that you will experience with this problem? The most common symptoms associated with a bad catalytic converter are probably the lack of engine power and the feeling that the car cannot breathe well. This is often caused by a clogged catalytic converter.

Also, there could be decreased fuel economy and a rotten egg smell. But why a rotten egg smell? Well, this is mainly the case because fuel contains a bit of sulfur. And is the task of the catalytic converter to tackle this sulfur and convert it. So, when the converter doesn’t work well, you will have problems like the rotten egg smell. But how you can diagnose the P0420 Toyota Camry code? Well, more about that, we are going to cover next.

How Do Diagnose P0420 Toyota Camry?

Now let’s dive into the P0420 Toyota Camry code and learn more about how you can diagnose this problem the right way.

The first thing you will need to do is to scan the car for codes. First, clear the codes with the OBD2 scanner and scan the car for codes. Pay attention to the ones that stick. If the P0420 sticks, then you know where to look. The catalytic converter.

But here is a big but. Also, check other codes as well. Mainly because a faulty O2 sensor can also cause this code. In addition to this, if the A/F ratio is not good, can also trigger the code.

If everything is well and you don’t have other codes, check for exhaust leaks and if you have leaks, fix them because they might be causing the problem.

And if everything is good, the last thing you need to check is the catalytic converter. And in order to do so, you will have to remove it from the vehicle. If the catalytic converter is badly damaged inside or it is clogged, it means that you will have to replace it.

And before you replace the catalytic converter, make sure that you check the spark plugs and see if your car is running rich or burning oil. Because if it does, then the chance of another catalytic converter failure is really big. So, fix things first and then replace the converter and then you will hopefully finally get rid of the annoying P0420 Toyota Camry code. Remember that these rules work for any car, it doesn’t matter if it’s a Camry or a Tundra or a Tacoma.

Cost To Fix P0420 Toyota Camry

So, we learned all about the P0420 Toyota Camry problem, but what about the price? How much money can you expect to pay in order to sort this problem out?

Well, if it’s a simple O2 sensor or an exhaust leak, you will get away with $300 or less. If the problem is bigger like a catalytic converter. Then you can expect to pay anywhere from $1,200 for the cheapest, up to $2,500 for the most expensive catalytic converters.

The cost of these components is crazy high and you need to make sure that your catalytic converter is always in good health. Drive your car frequently on long-range journeys to get the converter up to temperature and you will have no issues with it any time soon.


In this article, we have covered quite a bit when it comes to the catalytic converter and the P0420 code. First, we learned the basics of car diagnostics and how it is done.

Then we covered the P0420 problem and its meaning. We learned the causes, symptoms, and how you can diagnose it quickly and effectively. And also at what cost could that be done.