Replacing a damaged catalytic converter can be pretty expensive, hence why someone would consider bypassing it. Some car owners may also want to enjoy the increased horsepower that comes with driving without a catalytic converter. The catalytic converter or cat is a device in the vehicle’s exhaust system that changes harmful substances in your car’s exhaust fumes to a less toxic exhaust product via oxidation and reduction reactions.

The catalytic converter is made of metal with a ceramic honey-comb-like interior with insulating layers containing platinum, rhodium, and palladium that help with the redox process. Ironically, there are potential benefits to removing your car’s catalytic converter, such as increased horsepower, better gas mileage, lower engine temperature, more fuel options, and better exhaust sound. This article will help you with automotive knowledge of bypassing the catalytic converter and fixing converter issues without tampering with it.

Can a catalytic converter be bypassed?

Some situations will allow you to remove the catalytic converter and bypass it with a straight pipe. The engine may work more efficiently without a converter as it does not have to work too hard to push out exhaust fumes, but it is against state laws due to its contribution to air pollution. Bypassing should be a temporary fix, and you should look into buying a new catalytic converter for your vehicle soon.

Things You’ll Need

Bypass-pipe or test pipe
Hydraulic jack
Four Jack stands
Adjustable wrench
Penetrating fluid

Instructions

Drive the vehicle onto a level surface and put it on the parking brakes.
Lift the car with the hydraulic jack, lower it onto the jack stands and allow the exhaust system to cool off.
Go under the vehicle and spray some penetrating fluid onto the mounting bolts of the catalytic converter. Allow the penetrating fluid to work for about 15 minutes.
Disconnect the oxygen sensor wiring harness from the catalytic converter. Use an adjustable wrench to remove the sensor from the converter.
Use the adjustable wrench to remove the mounting bolts holding the catalytic converter into place. Place the catalytic converter on the ground.
Attach the bypass pipe onto the exhaust system where the catalytic converter was. Adjust the pipe until the bolt holes on the flanges of the bypass pipe align with those on the existing exhaust pipe.
Insert the catalytic converter mounting bolts into the holes in the flanges and tighten them with an adjustable wrench.
Reinstall the oxygen sensor into the fitting on your bypass pipe and tighten it into place. Plug the wiring harness into the sensor to reconnect it to the car’s computer.
Raise the car using a hydraulic jack, remove the jack stand and lower the vehicle onto the ground.
If your catalytic converter was defective, replace it as soon as possible.

The pros and cons of removing the catalytic converter

The pros

1. Increased horsepower

A significantly increased horsepower is a possible benefit when a car runs without a catalytic converter because it creates back pressure on the engine. The catalytic converter reduces the force that removes the exiting gases and consequentially decreasing the engine’s combustion. But when you remove the catalytic converter and replace it with a bypass pipe, the exhaust gases move faster, improving combustion and increasing horsepower.

2. Improved exhaust noise

When the catalytic converter works to filter the exhaust gases, it reduces the impact of exhaust gases flowing from the engine, which muffles the sound of the exhaust and the vehicle’s muffler. Without the catalytic converter, your vehicle produces the louder, low-pitched, and more notable exhaust sound that some car owners love. Arguably, the noise is also a disadvantage to other drivers.

3. Reduced engine operating temperature.

Without a catalytic converter, exhaust fumes exit the engine faster, which reduces the engine’s workload—reduced workload results in lower engine temperature. Lesser engine workload means there is less friction in the engine, which can help to reduce wear and tear of your car parts over time.

4. Improved gas mileage

There is less strain on your vehicle’s engine when you remove the catalytic converter since it restrains the removal of exhaust fumes. The reduced workload means the engine will produce the same amount of energy with lesser fuel consumption and better gas mileage.

The cons

1. It is illegal in the U.S.

The U.S federal government does not allow tampering with your vehicle’s catalytic converter unless it is damaged or missing, the car is from before 1996 and has more than 50,000 miles, or it’s from 1996 and later vehicle with more than 80,000 miles. The Environmental Protection Agency has set national guidelines that regulate the removal, replacement, and installation of the catalytic converter. In states like South Dakota and Florida do not have emissions testing. States like California have more strict rules, and driving around with no cat will earn you hefty fines of up to $10,000.

2. Pollutes the atmosphere

It can clean up to 90% of toxic fumes into less harmful gases. Even though removing your vehicle’s catalytic converter will not affect performance, you will still be releasing poisonous fumes into the air. These toxic fumes can also harm you and your car passengers if the fumes get into your car cabin with the windows closed.

3. It triggers a fault code.

Removing your vehicle’s catalytic converter will trigger a fault code. If your car has the check engine light on, it will light up on the dashboard display. Though you can fix the check engine light indicator by installing a spacer on your lambda oxygen sensor, you risk the light not working properly again, and it will not detect other issues using this indicator light.

4. It creates a louder noise.

Though some car drivers love the healthy noise on an exhaust system without a catalytic converter, the noise can be harmful. When you drive with your windows down and a full engine, you might receive an exhaust noise of up to 110 decibels. It exceeds the recommended sound level of 85 decibels which is potentially dangerous to hearing health. If the noise is not disturbing, it will still be loud enough to interfere with conversations.

5. Increased fuel consumption for some cars

Not all vehicles behave the same way after a catalytic converter removal. Some car owners report increased fuel consumption and reduced low-end torque. The reason for this is that the oxygen sensors stop sending correct readings causing more fuel usage.

To avoid any legal penalties, it is best to replace your damaged catalytic converter instead of bypassing it. We recommend replacing your catalytic converter with the same model and brand as the original one. You can also use aftermarket cats as long as they are EPA certified for your vehicle.

How do you know when you have a bad catalytic converter?

There are several ways to find out if you have a bad catalytic converter. The most obvious way is that the check engine light will flash to indicate a problem with the device. Other symptoms brought about by a bad converter include:

The check engine light will turn on
Slow engine performance
Reduced acceleration
Rattling noise when the engine starts
Excessive exhaust temperature
The smell of rotten eggs or sulfur from the exhaust
Overheating engine
Excessive heat under the vehicle
Dark exhaust smoke

When you scan the check engine light with a code reader and receive the P0420 or P0430 codes, the most likely problem is a faulty catalytic converter. But always confirm with your code reader manual and keep in mind that there may be several error codes that coincide with the one for a catalytic converter.

If you notice your engine misfiring too often, there may be a problem with a clogged converter. Driving your vehicle with a clogged catalytic converter will reduce your gas mileage and the overall performance of your engine. You will have to replace it otherwise it will damage your engine.

It would be best to fix the clogged catalytic converter immediately as it will cause slow engine performance and reduced acceleration. If you ignore the problem for too long, the converter becomes a fire hazard. A clogged catalytic converter becomes easily overheated can ignite surrounding flammable materials while it’s running hots. It also prevents the easy flow of exhaust fumes from the car resulting in a misfire.

How do you clear a catalytic converter code?

The P0420 error code indicates that the vehicle’s computer detects a catalytic converter issue. If the error code persists after bypassing the converter, you can clear the code by installing a spark plug defouler on the downstream oxygen sensor. Installing the spark defouler will permanently remove the catalytic code without tampering with the converter. This method also requires you to be having a working oxygen sensor.

The catalytic codes usually come from the downstream sensor located closer to the tailpipe and monitor how the converter works. Follow these steps to install a defouler and make the oxygen sensor think that the converter works properly, thereby clearing the error code.

Disconnect the car battery to reset the car’s computer and clear the catalytic converter error code.
Remove the downstream oxygen sensor and take it to a reputable car parts shop to get a compatible spark plug defouler. The threads on the oxygen sensor should match those on the defouler.
Measure the diameter of the tip of the oxygen sensor that runs past the threads. Choose a drill bit that is slightly larger than this diameter but smaller than the defouler threads.
Place the defouler in a vise and drill it off until the sensor can slide into the defouler. Don’t drill through the end of the defouler; it will increase the hole at the bottom of the defouler.
Screw the defouler into the exhaust pipe where the oxygen sensor sits and then insert the oxygen sensor into the defouler and rewire it.
Reconnect the car’s battery and start the vehicle. Check for any catalytic converter error code.

The cheapest way to fix a catalytic converter

Replacing a catalytic converter is very expensive because of the filtering metal it contains. Your catalytic converter’s efficiency can be affected by oil deposits and other contaminants. If your catalytic converter is not severely clogged or containing broken parts, you can get away with cleaning it. Cleaning the converter involves relatively affordable cleaning products and cuts down on labor costs as you can easily do it yourself.

To ensure this method will work, tap the converter with a mallet or wrench. Hit it hard enough to rattle it, but not so hard that you dent or break it. If you hear rattling on the inside, you may have broken components or heavy sediments, which you can only fix by replacing the converter. If you don’t hear any strange sounds, proceed with the following steps.

Cleaning without removing the catalytic converter

Get some fuel in a can and a catalytic converter cleaner. Some cleaners only work with diesel or gasoline engines, while others work with both.
Ensure your fuel tank has at least 15 liters of fuel. Pour the recommended amount of the cleaner into the fuel tank.
Start your engine and drive your vehicle. Driving will spread the cleaner to clean your exhaust system. The cleaner’s label will indicate how long you should drive for the best results.
Drive for about half an hour or as indicated on the cleaner’s label until the fuel tank is empty. Make sure the engine does not overheat.

Cleaning by removing the catalytic converter

If the catalytic converter code is still showing, there is another way to deep clean the converter by removing it.

Park the car on a flat surface, switch it off, and then allow it to cool down completely.
Raise the catalytic converter with a hydraulic jack and secure the car on the jack stands.
Disconnect the oxygen sensor with an oxygen sensor wrench.
Apply some penetrating oil around the bolts holding the converter onto the exhaust system.
Remove the converter and inspect it. Try shaking it, and if you hear a loud rattle, you should replace it. If there is little no rattle, proceed with cleaning.
Power wash the inside and outside of the catalytic converter to clean out all the dirt and debris.
Power wash the outlet and inlet pipes.
Mix hot washer and degreaser and soak the converter in the solution for one to two hours.
Take it out, rinse it with clean water, and allow it to air dry.
Reinstall the converter and the oxygen sensor.
Test drive the car and then check for the code.

Will removing a catalytic converter cause a check engine light?

Yes. Removing the catalytic converter or driving with a damaged one will trigger a fault code which will cause the check engine light on the dashboard to turn on and start flashing. The check engine light will flash after removing the catalytic converter because, without the catalytic converter, the downstream oxygen sensor on the exhaust pipe will detect unfiltered air, making the computer think the catalytic converter is faulty.

Check this too: Should I Check My Oil When The Engine Is Hot Or Cold?

Why is my check engine light still on after replacing the catalytic converter?

Typically, replacing your catalytic converter should clear the check engine light if it is well installed. Make sure the new catalytic converter meets the EPA requirements. It is best to get a new converter from the same make and model as the original one compared to a used one that will be cheaper but less efficient after a short while. In case the new converter doesn’t meet the standards the manufacturer shot for with the original unit, you might still get the check engine light (it’s conversion threshold will be lower than what the car’s computer expects.

If your new catalytic converter meets state standards, but the warning light persists, you could be dealing with another problem affecting the oxygen sensor. Other car issues that can trigger the P0420 code include:

Broken wiring connections to the oxygen sensors
There could be a leakage in the exhaust system, the muffler, or manifold.
A defective oxygen sensor.

Conclusion

Recently, manufacturers have made a lot of progress in making more efficient and reliable catalytic converters. If yours is severely damaged, bypassing it with a straight pipe is possible. However, replacing a damaged catalytic converter is the best solution that is eco-friendly. Bypassing it is also illegal to even states that have more lenient emission tests. Most modern car engines are tuned to have a converter; therefore, removing it will decrease horsepower and gas mileage while creating unnecessary noise.