Do Cars Need Catalytic Converters to Run?

If your car’s exhaust system is aged and road-worn, you may be nearing a time when you’ll need to replace the muffler, tailpipe, other pipes, or the catalytic converter, or all of the above.

You may have seen or heard cars running without a muffler or tailpipe, with the only problem appearing to be that they’re noisy. But, the catalytic converter is more mysterious. So, you may wonder if your car could still be driven and driven safely without the catalytic converter (a.k.a. the “cat”).

So, what will happen if your catalytic converter breaks or stops functioning properly? Can your car continue to run without it? Is it safe to drive without it? If the converter breaks down while you’re on the road, even if the car still runs, should you try to keep driving it? 

If so, how long can you drive a car without a catalytic converter before you must replace it? Here’s some helpful information about what to do if your car’s catalytic converter quits working.

What is a catalytic converter, and what does it do?

A catalytic converter (cat) is a device installed in the exhaust system of an automobile for the purpose of converting harmful vehicle emissions of carbon monoxide, oxides of nitrogen, and hydrocarbons into their relatively harmless chemical elements of carbon dioxide, oxygen, and water.

A catalytic converter also eliminates unburned gasoline, which means that without it, that gas spews all around and lets out a great amount of pollution from automobile exhaust.

The United States Clean Air Act passed in 1970 compelled auto manufacturers to reduce harmful emissions significantly from the cars and trucks they produced. The catalytic converter became the solution to meeting the newly imposed standards.

Early models of catalytic converters used a two-way vehicle emissions cleaning process until 1981 when the three-way conversion process made the earlier approach obsolete.

The two-way process had been efficient in oxidizing carbon monoxide and unburned hydrocarbons, but it had not been effective in converting nitrogen oxides. The three-way process used today enables a catalytic converter to:

  • Convert carbon monoxide (CO) down to its less-harmful component carbon dioxide (CO2
  • Reduce nitrogen oxides (NOx) down to their components nitrogen (N2) and oxygen (O2)
  • Convert unburned hydrocarbons (HC) to components of carbon dioxide (CO2) and water (H2O)

Where is your catalytic converter?

The catalytic converter is installed along with the exhaust pipe system between the engine exhaust manifold and the muffler.

  1. On one end, the catalytic converter is connected to the pipe that runs from the exhaust manifold (which collects exhaust gasses from the multiple engine cylinders into a single pipe).
  2. On the other end, the cat connects to the vehicle’s muffler (which muffles the noise of the combustion engine exhaust).

For a clearer frame of reference, at the end of the muffler opposite from the end connected to the catalytic converter, the tailpipe is connected (which routes the exhaust gasses away from the car).

How does a catalytic converter work?

The earlier design of three-way catalytic converters was the plus-air model, which less efficient than today’s commonly used without-air design.

This modern catalytic converter employs a three-way reactive processes to reduce and oxidize harmful engine emissions before releasing them into the atmosphere through the exhaust pipe.

As in the earlier design, today’s converter uses a combination of precious metals, platinum, and rhodium, to create a catalyst for the process of reducing harmful chemical emissions down to their less harmful and harmless components.

  • The modern converter works with a system for monitoring and controlling O2. The role of the converter itself is in causing a chemical reaction to store and generate the release of O2. 
  • This emissions conversion system uses O2 sensors to trigger the vehicle’s fuel mixture to oscillate between rich and lean conditions. The oscillating, together with the storage and release of O2 on the surface of the catalyst, enables all three harmful chemical emissions to reduce down to their nontoxic components. 

An OBDII diagnostic system is used in modern cars and trucks, notifies the vehicle driver if the converter is not functioning at an acceptable level of efficiency.

Could you drive without a functioning catalytic converter?

Your car will continue to run without a catalytic converter. A cat does not help the vehicle engine run.

The role of the converter is entirely limited to cleaning up the car’s engine emissions before they pass through the car’s tailpipe and out into the environment.

So, technically speaking, you can continue driving your car without a catalytic converter, just as people did before this emissions equipment became increasingly used back in the 1970s. However, although your car will run without the cat, is it advisable to drive it without it?

Should you drive without a functioning catalytic converter?

Since the catalytic converter rapidly was first installed as standard emissions control equipment on the majority of vehicles five decades ago, cat installation has become a requirement under federal and state laws since that time.

Today, virtually all vehicles operated on public roadways have a catalytic converter. Driving an automobile without a functioning converter, removing it, damaging it, altering it, or otherwise tampering with it comes with potentially serious consequences:

  • Legal consequences — Removing or disabling a catalytic converter is illegal. Crimes of interfering with the functioning of catalytic converters can be punishable with fines costing thousands of dollars, especially in states with the strictest auto emissions laws (such as California’s famous CARB statutes).
  • Emissions testing failure — The absence of a catalytic converter will cause an automobile to fail the emissions test required for the renewal of vehicle registration.
  • Auto performance issues — If a converter is operating inefficiently, you may be able to continue driving the car without much risk of it breaking down. But, if the converter becomes clogged or severely damaged, the vehicle engine may stall or lose power, which can make driving the car difficult or even impossible.
  • “Check Engine” light — Removing a catalytic converter from a vehicle will activate the “Check Engine” light and cause it to remain illuminated until the converter is recognized again.  

How long can you drive your car without a catalytic converter?

A missing catalytic converter is a very different situation than having a malfunctioning one:

  • Missing catalytic converter — If the catalytic converter for your car has been removed or disabled, without causing any damage to other functional components of the vehicle, you can expect to be able to continue driving your car indefinitely without negative effects to its functioning or risk to safety. However, remember that it is illegal to operate the vehicle without the converter in place.
  • Malfunctioning catalytic converter — If the cat has developed internal problems, it can lead to poor engine performance and even to potential damage to other functional parts of your vehicle. It could even become a fire hazard. A converter that is not working properly also, of course, causes increased harmful emissions into the environment.

So, whether your catalytic converter is missing or malfunctioning, you should have it replaced as soon as possible to ensure legal compliance, optimum vehicle performance, and safety.

Is it safe to drive a vehicle without a catalytic converter?

There’s also a major difference in safety considerations between driving without a catalytic converter on your vehicle vs. driving with a cat on it that is malfunctioning or no longer working at all:

  • Missing catalytic converter — As discussed above, you can safely continue driving a vehicle without a catalytic converter, though it is illegal to do so and allows harmful emissions into the environment.
  • Malfunctioning catalytic converter — If the cat is deteriorating or broken, depending on the nature of the problem, the vehicle may or may not be safe to drive. Damage to other parts of the car is possible, which may lead to safety problems. If the heat inside the converter or surrounding exhaust system components escalates to extremely high temperatures, due to a faulty cat, there may be increased risk of a vehicle fire. So, you should replace a malfunctioning converter as soon as possible.

What are the symptoms of a malfunctioning catalytic converter?

There are various warning signs that your car’s catalytic converter is malfunctioning or is no longer working. The most common symptoms of a faulty catalytic converter include:

  • Vehicle is difficult to start or will not start
  • “Check Engine” light or “Service Engine Soon” light is on
  • Engine stalling out
  • Weak acceleration

Typically, the only clue that a catalytic converter has stopped functioning is that the “Check Engine” light is on. However, if the cat is clogged or blocked, causing emissions to be impeded from flowing freely through the device, then problems like difficulty starting, engine stalling, and poor acceleration can occur.

Can a car’s engine performance improve without a catalytic converter?

Yes and no. A vehicle can run with increased efficiency and power without a catalytic converter and without a muffler as well. Because a vehicle car’s engine can generate only a limited amount of power, placing an obstacle like a catalytic converter or a muffler in the exhaust pipe system impedes the exhaust gasses from freely escaping.

But, consider the negative impacts of poor exhaust control on other aspects of a car’s performance.

  • YES — On the one hand, the engine must utilize some of its power to push the exhaust out through those impeding exhaust control devices. Removing the catalytic converter and/or the muffler increases the car’s engine power to accelerate the velocity of the car’s motion and to travel more miles per gallon of fuel.
  • NO — On the other hand, if you eliminate too much of a car’s exhaust system, the consequence can be that some gas is being pulled out from the cylinders before it has actually burned, which decreases the car’s power and full efficiency. (Without the full exhaust control apparatus, the ideal length of the exhaust pipe would vary from one car to another, as needed to help compensate most effectively for the minimalized exhaust control system.)

So, yes, cars could run with more power and fuel efficiency without mufflers and cats. But, no, the vehicles would not perform as well. Overall, in terms of the way we need automobiles to work within our environment.

The best way to proceed, if  your catalytic converter is missing

Maximizing engine power and gas mileage to the extent of sacrificing the priorities of minimizing environmental pollutants by removing a catalytic converter may be appropriate in certain special circumstances.

But, for the vast majority of general purposes, the minute amount of power lost by routing emissions through a catalytic converter is understood as an entirely worthwhile trade-off.

Since you can drive your car without a catalytic converter, even though it’s illegal to do so, the best approach to take if your converter is missing (vs. malfunctioning) is to operate the vehicle as infrequently as you can and make only the shortest possible trips each time, until you get the part replaced.