P0420 Code-Meaning, Causes, Symptoms, Repair Cost, How To Fix?

Every car lover is fond of his cars, but it turns out into a liability. What if your car displays a p0420 code on your code reader and your car’s check engine light comes on, do not panic.

This article will help you understand what this error code means, what could be causing it and how to fix it.

What Does The P0420 Code Mean?

The most common cause of a p0420 is a bad catalytic converter. It can be caused by anything from a faulty oxygen sensor to a rich or lean running condition or misfires. Because there are so many variables that could cause this code. A catalytic converter has two oxygen sensors the front and back, or upstream and downstream, respectively. Their job is to make sure the catalytic converter is operating at peak efficiency.

When these sensors work properly, they operate in tandem. The front sensor’s readings typically fluctuate, while the back sensor’s readings remain steady. These sensors should never read the same or similar to each other. When they do, they generate the p0420 code. An incorrect air-fuel mixture can also temporarily or permanently reduce the efficiency of the catalyst. Which results in a pO420 trouble code.

What Are The P0420 Symptoms?

The most common symptom of code P0420 is a check engine light on the dashboard. In some rare cases, you may also notice issues like:

1. Loss Of Power:-

There are many reasons why your vehicle may be losing power, especially when accelerating. Some of these common causes are Mechanical problems such as Low compression, clogged fuel filter, dirty air filter, and clogged Exhaust Manifold.

2. Slow Acceleration:-

Sluggish acceleration could result from a failing fuel pump, or it could be a malfunctioning sensor. If you are driving down the road and notice your vehicle has sluggish acceleration, it could be due to two reasons. You could be running out of fuel, or your car doesn’t have enough power.

3. Sulfurous Smell From The Exhaust Pipe:-

The smell comes from the small amount hydrogen sulfide, or sulfur, within the fuel. Hydrogen sulfide is usually converted into odorless sulfur dioxide. However, when something breaks within the vehicle’s fuel or exhaust system, it can inhibit this process and create the smell.

4. Decreased Fuel Economy:-

One of the most common culprits for a drop in fuel efficiency is dirty fuel injectors. Fuel injectors are the nozzles that spray fuel into each engine cylinder. A fuel injector’s spray pattern must be very precise to properly mix with air and combust inside the engine.

5. Check Engine Light Is On:-

When your vehicle’s computer believes there is a problem that could affect your car’s emissions control system. When the light comes on, code p0420 diagnostic trouble code will stay there even if the light goes out.

Hence, these are some symptoms of p0420 code.

What Are The Causes Of Code P0420?

Many problems can cause code P0420 to appear during a diagnostic check, which makes it difficult to fix. There are other potential causes for this code. It’s important to look for other codes that could indicate the root cause of converter failures, such as misfires or an incorrect air-fuel ratio.

1. Damaged Muffler:-

The broken muffler can reduce the effectiveness of your exhaust system. The broken part can keep your car from being effective when siphoning the exhaust fumes out of your engine and will negatively affect your car engine’s performance. In turn, your car will produce higher emissions and lose fuel economy.

2. Damaged Exhaust Manifold:-

The exhaust manifold is the part of your car connecting the engine to the exhaust system. It’s responsible for collecting all the exhaust and funneling it into the catalytic converter and then onto the muffler and tailpipe. Even though most exhaust manifolds are made of cast iron or stainless steel, they are not indestructible. Over time, they can crack due to constant, extreme temperature fluctuations, leading to unpleasant symptoms or even permanent engine damage.

3. Damaged Exhaust Pipe:-

If you have an excessively noisy engine or a faulty exhaust manifold gasket, it will cause an exhaust leak that sounds like a hissing or tapping sound. The sound is especially loud during a cold start or when you accelerate the vehicle. Driving on rough roads can cause your exhaust system to be subject to shaking and bumps that can cause holes and structural components to weaken, while rust and corrosion damage in exhaust system parts are perfect places for exhaust leaks to form.

4. Engine Misfire:-

An engine misfire is caused when one or more cylinders doesn’t produce power, and there are several possible causes, from a fouled spark plug to a clogged fuel injector or faulty oxygen sensor.

5. Contaminated Oil In The Catalytic Converter:-

The catalytic converter can also be damaged by evaporated engine oil. Oil vapors usually stay inside the engine. But, excessive amounts of vapors get carried into the combustion chamber where they mix with the fuel. Since the oil vapors are heavier than the fuel, they fail to burn completely.

Hence, these are some causes of code p0420.

Is Code P0420 Serious?

You should resolve any issue that causes your check engine light to turn on as soon as possible, as these problems can have disastrous consequences. Code P0420 primarily causes drivability issues.

The only thing that could potentially happen is that the catalytic converter is so damaged that the catalytic converter’s internal parts come loose and block the exhaust flow, which is pretty unlikely to happen though.

But, the P0420 trouble code could make your car’s emissions bad, which is bad for the environment, so you should fix it as soon as possible.

How Much Does It Cost To Fix Code P0420?

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time.” Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your p0420 code.

How To Fix The Trouble Code P0420?

1. The only fix for the problem is to replace the catalytic converter. However, many other issues can arise with a catalytic converter issue. You must also take care of those issues before installing a new catalytic converter, or the damage may worsen.

2. If your catalytic converter has damage, it will continue to harm other areas of your vehicle. Make sure to get your repair from a business known for its thorough diagnostic checks.

3. Pay close attention to the exhaust manifold, gaskets, and exhaust pipes pre-catalytic converter. If any leaks are found, repair the leak, clear the code, and complete several drive cycles to verify that was the fix.

4. Check for any other trouble codes with your diagnostic scanner. If you find codes like P0300, P0301, P0302, and P0303, etc. You have a misfiring engine and the misfires may cause the P0420 error code. In this case, you should fix the misfires first, clear the codes and see if the P0420 code comes back.

5. If you find DTC codes like P0171, P0172, P0174, or P0175, it means that your engine is running rich or lean. This could be due to a faulty fuel injector, high or low fuel pressure, MAF sensor, engine coolant temperature sensor, or almost any faulty engine sensor. The air-fuel mixture needs to get addressed and then see if the P0420 code comes back.

Hence, you can try these fixes to clear the code from the code reader of your engine.


We hope the above-mentioned information about the p0420 code will be helpful to all the readers. If anybody’s doubts persist feel free to comment in the comment section below. We’ll try to solve your doubts as soon as possible.

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