Bad Catalytic Converter Symptoms, Can You Drive a Car With a Bad Catalytic Converter?

The main purpose of a catalytic converter is to remove carbon monoxide as well as other toxic gases. This is a crucial part of an exhaust system and is located between the muffler and car's exhaust manifold. Most of the cars today come with a single catalytic converter, but some with dual exhaust systems come with two catalytic converters. This is one catalytic converter for every pipe. Some modern vehicles come with two catalytic converters, and this helps further lower harmful emissions.

The catalytic converter filters or converts all the harmful emissions such as carbon monoxide, nitric oxide, and hydrocarbons before these are sent into the atmosphere.

After you start your car, toxic gases produced by the engine will move through the catalytic converter.  If you look closely, the structure of a catalytic converter is similar to a honeycomb and is made from metals like rhodium, platinum, and palladium.

During high temperatures, a catalytic converter will function at 800 degrees Fahrenheit.  At this temperature, a chemical reaction happens where the dangerous gases are filtered by the cat, and safer compounds come out like water, oxygen, and carbon dioxide.

How to tell if the catalytic converter is bad? Catalytic converters last a lifetime, but sometimes, it may become clogged or bad, and thus, needs to be replaced. Here are some of the symptoms to watch out for.

1. Check Engine Lights Flashes

Most new cars come with oxygen sensors. These sensors can determine if the exhaust gases are not catalyzed properly. The sensor sends information on the car’s onboard computer system, and this triggers the check engine light symbol on your dashboard.  

Also, in most modern cars, you’ll find codes P0420 or P0430 flashing on your screen. These codes mean your vehicle has a problematic catalytic converter.

Read Next: oxygen sensor bypass

2. Rotten Egg Smell Coming From the Exhaust

Another symptom of a bad catalytic converter is the smell of rotten eggs coming from your car exhaust during combustion.

This is from the gasoline that's not able to combust properly. 

The fuel contains minimal amounts of sulfur that change to hydrogen sulfide during combustion. Working catalytic converters can convert the hydrogen sulfide to sulfur dioxide, an odorless gas, while bad catalytic converters may not be able to convert these gases causing the smell to leak from the exhaust.

3. Bad Acceleration

When you have a bad catalytic converter, your engine won't be able to work properly, leading to poor power. This is mostly seen when you try to accelerate. When there is thick carbon buildup in the cat's honeycomb system, there will be a partial blockage in the converter. Usually, a clogged catalytic converter causes a misfire.

One of the most leading failures of a catalytic converter is clogged. Your car's engine needs a good, patent exhaust flow to accelerate, but when the catalytic converter is clogged, there will be a lack of acceleration power when you ride up a hill or when you have a heavy load. When there's clogging, you have no choice but to replace your catalytic converter. In some cases, a catalytic converter clog cleaner may also help.

4. Emission Test Failure

What problems can a bad catalytic converter cause? In some states and countries, your car must pass an emission test to prove that it's roadworthy. If you have a bad catalytic converter, your car won't have a chance to pass an emission test.

5. Loud Rattling Noises

Pieces of broken catalytic converter material can break apart because of too much heat or excessive damage. This is very noticeable as these pieces will move around your car's exhaust as you drive or as you remain idle. Usually, the noise is very loud upon starting your car.

If this is one of the bad catalytic converter symptoms you’ve noticed, then we recommend replacing your catalytic converter right away. These small chunks of material can move further into the exhaust system and possibly through the muffler. When this happens, your car can stall or may not start at all.

Related: Muffler vs. Resonator

6. Poor Fuel Efficiency

A blocked catalytic converter will reduce the airflow that's needed to burn fuel. Thus, you will be forced to use the gas pedal more to accelerate. This will lead to more fuel injected into the cylinders and will cause your car to have more fuel mixture than you need. 

If you notice you're filling your tank up more often, then you may suspect problems with your catalytic converter.

Related: How to gut a catalytic converter without removing it

7. Your Car Won’t Start

Will a clogged catalytic converter cause loss of power? Your car can stall when pieces of the catalytic converter honeycomb material become stuck in the muffler. Also, a severely stuck catalytic converter can lead to exhaust back pressure that can prevent your engine from starting.

Can a car run with a bad catalytic converter? You may still drive your car during the early stages of catalytic converter failure. But as your catalytic converter condition worsens, it may be dangerous to drive your car. Also, if your car fails an emission test, it is likely you won’t be allowed to drive your vehicle at all.

Final Words

Now that you know the bad catalytic converter symptoms, you're on the road to keeping your catalytic converter more efficient and in good working condition. If you notice any of these symptoms, have a certified technician/mechanic, check your car right away. He will diagnose your vehicle and determine if you need to replace your catalytic converter or if you have other car exhaust problems.