Bad Catalytic Converter Symptoms, Causes, And Replacement Cost

The catalytic converter is the most important part of modern vehicles. It helps to control the exhaust emissions. It is installed in the exhaust system between the muffler and the engine. It uses ceramic-coded beads and a variety of precious metals (catalysts) to transform pollutants such as nitrogen oxides and unburned gases into nontoxic gases. This article mainly explains the bad catalytic converter symptoms, causes, and replacement cost.

What is a Catalytic Converter?

A catalytic converter is a mechanical unit that converts toxic gases emitted from the IC engine into less-toxic pollutants by catalyzing a redox reaction. The catalytic converter is also known as a ‘CAT’.

Catalytic converters are usually used with internal combustion engines fueled by gasoline or diesel, including lean-burn engines, and sometimes on kerosene heaters and stoves.

Catalytic Converter

A catalytic converter is an important part of the vehicle’s emissions system. It is designed to extend the life of the vehicle but can fail if it becomes clogged. It has a honeycomb structure.

The honeycomb structure is designed to allow contaminants to flow over more exposed surfaces, converting hydrocarbons, carbon monoxide, and nitrogen oxides into less hazardous elements like carbon dioxide. Platinum is a costly product but is often utilized as a catalytic converter.

Symptoms of Bad Catalytic Converter

As the catalytic converter goes bad, it gives one of the below-given symptoms:

  1. Check engine light illumination
  2. Rattling noise
  3. Smell of Sulfur
  4. Poor acceleration
  5. Engine misfiring
  6. Black smoke from the exhaust pipe
  7. High fuel consumption
  8. Failed emission test
  9. Engine Stalling
  10. Increased emissions

1) Check Engine Light Illumination

The illuminated check engine light is one of the most common symptoms of a faulty catalytic converter. This light is located on the dashboard of your vehicle. The car dashboard contains multiple warning lights and symbols.

The latest cars also have oxygen sensors. These sensors observe the efficiency of catalytic converters by monitoring the exhaust gas level in the exhaust system.

check engine light

As the oxygen sensor observes that the exhaust gas is not being properly catalyzed, it sends a signal to the “Check Engine Light,” and the engine light starts illuminating. This light may also illuminate due to many other reasons, such as engine overheating, low coolant level, etc.

One of the best methods to get the car trouble code is to use a diagnostic scan tool. P0430 and P0420 trouble codes are two famous trouble codes that represent catalytic converter failure.

Read More: Causes of Check Engine Light Flashing 

2) High Fuel Consumption

Poor fuel economy is another famous symptom of a bad catalytic converter. Better fuel mileage sounds good enough, but it may badly damage the engine and lead to a costly repair.

Poor fuel economy, symptoms of bad Catalytic Converter

In the case of a clogged exhaust system, the fuel doesn’t combust efficiently in the combustion chamber; due to that, engine efficiency reduces, and it needs to work harder to meet the power requirements. So, in general, a defective catalytic converter uses more fuel, but in some cases, it uses low.

3) Rattling Noise

Rattling Noise due to bad catalytic converter

When the parts of the catalytic converter become cracked due to engine overheating or damage, it may start producing a rattling noise coming from beneath the car. This noise usually becomes very high during the startup of the vehicle.

4) Rotten Eggs Smell

Rotten Eggs Smell

The sulfur or rotten egg smell is one of the common signs of catalytic converter failure.

As the converter is blocked, exhaust gas flow is restricted, and the engine’s fuel-air mixture becomes rich (if there is too much fuel, the fuel does not burn). Combustion of this excess air-fuel mixture can produce an odor similar to burning sulfur or rotten eggs.

5) Poor Acceleration

acceleration problems

The engine’s poor acceleration is one of the major symptoms of a blocked catalytic converter. In such a situation, the engine couldn’t produce power according to the vehicle’s requirements.

The catalytic converter usually clogs due to the excessive carbon build-up in the honeycomb structure, or internal components begin to melt due to excessive heat from unburned fuel.

For efficient performance of your engine, the exhaust system of your engine must be good and shouldn’t be clogged. As the converter goes bad, you will observe poor acceleration issues.

6) Increased Emissions

Increased Emissions

An increase in exhaust emissions is one of the clear symptoms of a bad catalytic converter. The main function of the catalytic converter is to reduce the emission of harmful gases.

As the catalytic converter clogs or damages, it doesn’t perform its job efficiently, and the exhaust gas emission rate increases. This leads to increased engine emissions in the vehicle.

In case of a bad converter, your vehicle may also expel black exhaust smoke from the tailpipe when accelerating it.

7) Engine Misfiring

Engine Misfiring due to bad catalytic converter

When the catalytic converters become clogged, the oxygen flow into the engine becomes restricted, and the engine requires large amounts of oxygen for efficient combustion of the fuel. In such conditions, a large amount of unburnt gases are collected that can cause engine overheating and can also cause the engine to stall.

When your engine starts misfiring, you must repair it immediately because it may lead to a costly repair.  

Read More: Engine Overheating Causes and Symptoms

8) Failed Emission Test

Failed Emissions Test

A failed emission test is one of the common signs of a bad catalytic converter. When your catalytic converters go bad, they don’t control the emissions efficiently, which may result in a failed emission test.

9) Black Smoke from Exhaust Pipe

Black Smoke from the Exhaust Pipe

When your catalytic converter goes bad, the exhaust gases start accumulating in the exhaust. As they gathered in high quantities, they became thicker, and their color became dark. Therefore, if your vehicle is emitting dark smoke, it means that your catalytic converter is damaged.

10) Engine Stalling

engine Stalling due to a faulty catalytic converter

The engine can burn too much fuel if the catalytic converter is clogged. It also creates back pressure, making it difficult for the engine to escape exhaust gases.

If your car stalls 2-3 seconds after starting, it may be due to a clogged converter. This is because it can take a few seconds for the pressure in the exhaust system to build up before the engine stalls and shuts down.

Read More: Engine Stalling Causes and Prevention

Causes of a bad Catalytic Converter

The catalytic converter is one of the most important parts of the IC engine vehicle. Your catalytic converter may go bad due to different causes, including physical wear and tear, contamination, an exhaust system leak, poor fuel quality, poor engine maintenance, bad O2 sensor, engine misfires, coolant leaks, physical damage, and age.

  • Age and Wear
  • Poor Installation
  • Poor Engine Maintenance
  • Poor Fuel Quality
  • Short Trips
  • Faulty Oxygen Sensor
  • Contaminants
  • Coolant Leak
  • Physical Damage

1) Age and Wear

The age of the catalytic converter is one of the most common causes of a bad catalytic converter. Your catalytic converter wears out with time due to exposure to high temperatures and pollutants in exhaust gases. With the age of your converter, its ability to control the toxic emissions reduces and can cause different issues.

2) Poor Installation

A catalytic converter that is not installed properly may lead it to go bad early.

3) Poor Engine Maintenance

Your engine requires regular maintenance to perform efficiently. If you don’t maintain your IC engine properly, it starts to burn oil due to wear on cylinder walls, firing pin rings, and valve guides.

This burned oil generates harmful elements that may badly damage your converter. Improper air-fuel mixture may also cause a bad converter. These factors can damage not only the inverter but also other motor components.

4) Poor Fuel Quality

Poor fuel quality or high sulfur fuel may cause premature catalytic converter failure.

5) Short Trips

If you have only used the car for short trips, your catalytic converter will not be hot enough to fully burn the hydrocarbon.

If your vehicle’s hydrocarbons don’t burn completely, they may ultimately clog your converter. To avoid this, drive the car for a long time to get the converter hot enough to completely burn off the hydrocarbons.

6) Faulty Oxygen Sensor

The oxygen sensor plays a big role in controlling exhaust emissions. The powertrain control module (PCM) also uses the data of the O2 sensor to regulate the air-fuel ratio.

When your O2 sensor goes bad, it sends incorrect emissions readings to the PCM. This wrong reading results in an incorrect fuel-air mixture. If your vehicle’s air-fuel mixture is too rich, unburned fuel will enter the converter.

If the mixture is too lean, the converter will be unable to convert the hydrocarbons into safe elements, which may cause the emission test failure.  

Read More: O2 Sensor Working and Location

7) Contaminants

Many contaminants have the ability to damage catalytic converters badly. These contaminants include carbon deposits, transmission fluid leads, internal coolant leaks, or engine oil. The contaminant coats the surface of your catalytic converter and prevents it from breathing accurately.

The contaminant blocks the small passageways and deactivates catalytic converters.

8) Coolant Leak

The coolant leak is one of the most famous causes of a faulty catalytic converter. An antifreeze or coolant leak in the combustor may cause different serious issues.

Insufficient coolant may also lead to engine overheating and blown head gaskets. If the leak reaches the exhaust system, it clogs the catalytic converter and prevents it from working efficiently.

Read More: Coolant Leak Symptoms and Causes

9) Physical Damage

Your converter must be physically fit for optimum performance. A catalytic converter is believed to last up to 8 to 12 years or even a lifetime. This service life is usually reduced when your converter is physically damaged. Your catalytic converters may damage due to multiple causes.

The following are the most common causes of the catalytic converter’s physical damage.

  • Speed bump
  • Poor construction material
  • Thermal shock
  • Corrosion
  • Bad driving conditions
  • Road debris and impacts

Catalytic Converter Location

A catalytic converter is usually located between the exhaust manifold and the muffler on the exhaust pipe system.

Catalytic Converter Location

The location of the catalytic converter varies according to the car model. Because in different vehicle models, the mounting distance of the converter to the engine is very different.

In some vehicle models, the catalytic converter is located in the middle of the tailpipe, while in other models, it may be mounted directly on the exhaust manifold.

How to Fix a bad Catalytic Converter?

As we discussed earlier, your catalytic converter may go bad due to different reasons. If your catalytic converter is bad and you want to fix it, then follow the below-given steps:

1) Fuel Additives

One of the simplest methods to fix a clogged catalytic converter is to use a fuel additive. The fuel additive helps your engine run more smoothly and removes carbon deposits from your converter.

For example, if you drive a car that runs on low-octane fuel, switching to higher-octane fuel can fix the issues related to the converter.

2) Fix the Physical Damage

Physical damage to the catalytic converter is one of the most common reasons for its failure. Try your best to prevent your converter from damage.

If your converter is damaged physically, you should fix it as soon as possible. If the damage can’t be repaired, you should replace your catalytic converter to prevent the engine from severe damage.

3) Italian Tune-Up

An Italian tuning method is utilized to fix many problems on vehicles. You may also fix a bad catalytic converter through this method. For this method, firstly, you need to push the car hard for the converter to be fully audible. After this, heat your converter to a high temperature between 427°F (427°C) and 1000°C (1832°F).

After heating, drive your car more than normal to burn off carbon deposits accumulated in your intake valves, cylinder heads, oxygen sensors, and catalytic converters. However, this method will not work if your converter is heavily clogged.

4) Fix Exhaust Issues

As we discussed above, exhaust leaks are common and may lead to the failure of the catalytic converter and oxygen sensor. Close inspection can reveal an exhaust leak. The repair of the exhaust leak may “restore” the functionality of the catalytic converter.

Corroded hoses and worn exhaust gaskets are the most common problems that are much cheaper and more efficient than replacing your converter. Therefore, you must inspect the exhaust gaskets and engine hoses before replacing the converter.

5) Catalytic Converter Cleaning

If your catalytic converter is clogged, you should clean it properly. To clean the catalytic converter, follow the below-given steps:

  • Locate the converter. Follow the instructions written in the vehicle manual to locate the converter easily.
  • After locating the converter, remove it safely.
  • Use a pressure washer to remove any contamination from the matrix.
  • Wash the device from both sides.
  • After cleaning, wipe the unit with a clean cloth.
  • Reinstall the unit and run the engine to check its performance.

You can also follow the below-given method to clean or unclog a clogged catalytic converter:

  • Soak the catalytic converters overnight in a mixture of detergent and hot water.
  • This method may take a long time, but it is necessary to dissolve the contaminants that are blocking the converter.
  • After soaking or cleaning the converter, allow it to dry completely before installing it.

Catalytic Converter Replacement Cost

The replacement or repair cost of the catalytic converter varies according to the vehicle model, your living area, and the labor cost.

The average replacement cost of the catalytic converter is from $940 to $2470, including parts and labor. The catalytic converter cost itself can be up to $2260 of that.

FAQ Section

What repairs can fix the catalytic converter?

  • Cleaning the clogged catalytic converter
  • Proper installation of the converter
  • Replacing the faulty converter
  • Proper maintenance of the engine
  • Changing the fuel if needed
  • Fixing the issues that occurred due to short trips
  • Replacing the faulty oxygen sensor
  • Removing the accumulations
  • Fixing the coolant leak

What is the average life of a catalytic converter?

The service life of the catalytic converter depends on different factors, such as the converter maintenance, type of brand, vehicle driving condition, driving method, and converter construction material. The average service life of a catalytic converter is approximately 100,000 miles or 10 years. Many catalytic converters extend the life of your vehicle, but some offer regular service when the catalytic converter is replaced.

What is the Catalytic Converter function?

The main function of the catalytic converter is to convert toxic gases emitted during the operation of the internal combustion engine into water and less harmful pollutants by catalyzing a redox reaction. It stops the emission of harmful gases from the vehicle engine to the environment. Fully electric cars don’t have catalytic converters because they don’t use the internal combustion engine to generate power.

What happens when the catalytic converter goes bad?

The main purpose of your car’s catalytic converter is to control vehicle emissions and prevent air pollution. When your catalytic converter goes bad, it produces different symptoms such as check engine light flashing, poor acceleration, poor fuel economy, black smoke from the exhaust pipe, sulfur smell from the engine compartment, or a failed emission test.

Can I drive with a bad catalytic converter?

The issues related to the catalytic converter usually don’t affect the performance of the car. However, passing the emission test without a converter is very hard. You shouldn’t drive your car with a clogged or bad catalytic converter. A defective catalytic converter can produce higher emissions than your state allows. Therefore, in some countries, you can’t drive your vehicle without passing the emission test.  

What does a bad catalytic converter sound like?

A bad catalytic converter usually generates a rattling noise. However, you may hear a rattling noise because of the failure of some other engine parts. Therefore, a certain noise coming from the exhaust doesn’t always indicate an issue with your catalytic converter.

Can a bad catalytic converter ruin the engine?

Yes, your engine can be ruined due to faulty catalytic converters. However, the engine will most likely not run and will turn off until the faulty catalytic converter is repaired. The faulty converters may cause high engine back pressure, which may lead to the failure of the other engine parts and exhaust system.

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