What Are the Signs of a Bad Catalytic Converter?


Sep 10th, 2021

What Are the Signs of a Bad Catalytic Converter?

Catalytic converters play a crucial role in your car's exhaust system and are responsible for cleaning the emissions coming out from the engine. As a car owner, you should learn how to recognise the tell-tale signs of a converter going bad.

Some signs of a bad catalytic converter include the Check Engine indicator lighting up on your instrument panel, rattling noise from the engine, and a loss in fuel efficiency. Engine misfires and erratic driving also result from the same problem. 

Catalytic converter cleaners might help in some situations, but you'll likely need to replace the part. Thankfully, you can recycle your old converter for some money.

In this guide, you’ll learn how to spot signs of a bad catalytic converter and what you can do to resolve the issue.

Let’s get started!

Catalytic Converters 101: What They Are and What They Do

Before we dive into the symptoms of a bad catalytic converter, we’ll need to brush up on our knowledge about what it is and what it does. In doing so, you’ll better understand how a failed catalytic converter causes so many problems for your car.

A catalytic converter is part of an automobile's exhaust system. As the combustion process takes place in the engine, it produces and releases harmful gases and other emissions into the atmosphere.

These toxic emissions need to be 'cleaned', or in this case 'converted', into less harmful substances.

That’s where the catalytic converter comes into play. As the emissions flow out of the engine, they’ll pass the converter and change into relatively harmless gases and steam. Then, the emissions will flow out of your exhaust pipe safely and into the surrounding environment.

Common Signs That Your Catalytic Converter Is Bad

Here are a few signs that may suggest problems with your catalytic converter.

1. Check Engine Light

The most common sign of catalytic converter trouble is the Check Engine light on your instrument panel lighting up. However, you also need to understand that this light will turn on for many different reasons, so don’t be quick to assume that the converter is the issue every time it happens.

Instead, troubleshoot the issue by looking for other tell-tale signs that come with the Check Engine warning. 

2. Rattling Noise from Engine

While the Check Engine light is on, listen for a rattling noise coming from the engine. You can do this while in the vehicle or keep the engine running and inspect under the hood and the vehicle’s underside.

Here’s how a failed catalytic converter can cause that rattling noise:

  • Excessively rich fuel-air mixtures will not burn thoroughly inside the engine during the combustion process.
  • The emissions from that problematic burning will flow to the catalytic converter and cause damage to it.
  • Inside the catalytic converter is a honeycomb mesh coated with catalyst materials. This mesh can get damaged, collapse and break as a result of the inappropriate air-fuel mixture.

The rattling noise you hear comes from those broken parts shaking around inside the catalytic converter.

3. Lower Fuel Efficiency

The catalytic converter connects directly to the engine. When the converter is damaged or not working correctly, it can create backpressure, making the engine lose its efficiency.

As a result, you will experience less fuel efficiency than usual. In simpler terms, you’ll end up using more fuel than you usually do. That is because the engine will use more fuel than usual to produce the same amount of energy.

4. Engine Misfires

At this point, it’s clear that the catalytic converter can affect the combustion process that’s happening inside the engine. Another way it can do that is cause misfires inside one or more engine cylinders.

The reason for this is very straightforward. A blocked or damaged catalytic converter will restrict airflow. And as mentioned earlier, back pressure will affect the combustion process’ ability to happen efficiently inside the engine.

Engine misfires can also lead to more damage, as unburnt fuel can pass through and reach the catalytic converter, damaging it further.

5. Unstable Driving

Unfortunately, problems with your catalytic converter don’t just affect the engine’s fuel efficiency, but they can also lead to unstable driving. Common symptoms that you might experience include:

  • Your car jerks forward when driving
  • Your car stalls
  • You find that you lose fuel as you’re accelerating

Can You Just Clean a Clogged Catalytic Converter?

Like most people, you’d probably groan at the thought of having to replace your catalytic converter. The part is a significant component, and it doesn’t come cheap, no matter what car brand or model you drive. So, is cleaning a catalytic converter an option if it’s just got a clog but is otherwise free from damage?

Yes, you can use a catalytic converter cleaner if the clog is not severe. This approach will help if the blockage is minor or moderate but will not be very effective on something more severe.

When Should I Replace My Catalytic Converter?

If the damage or wear is extensive, you will have to replace your catalytic converter entirely. Considering catalytic converter prices these days, it’s understandable that you’d want to be sure it’s an absolute necessity before you go out and buy a new one. So, here are some clear indicators that your converter is past the point of no return and must be replaced:

  • Damaged: If the catalytic converter is damaged (not merely clogged), you must replace it. This component is not repairable. It’s only replaceable.
  • The cleaner doesn't work: If using catalytic converter cleaning products does not help, that’s a sign that the blockage is too severe. That’s a clear sign that a replacement is necessary.
  • More than ten years old: You can expect a catalytic converter to last approximately ten years. If the one in your car is older than that, you may as well get a new one.
  • Mechanic’s advice: Sure, your mechanic has an incentive to get you to buy a replacement. However, that’s no reason to discount their opinions and recommendations. If considering all of the above, your mechanic tells you a replacement is necessary, it’s a good idea to listen to them.

Can You Recycle Your Damaged Catalytic Converter?

Yes, you can recycle your damaged catalytic converter. You can view that as being the silver lining in all of this. 

As we’ve seen in our previous article, catalytic converters are still worth a bit of money even when they’re unusable. So, one way of looking at it is that your bad catalytic converter can help subsidise your purchase of a brand-new replacement. So, by scrapping it, you’ll be helping the environment and yourself at the same time! 

Finding buyers for your scrapped converter? Check out the wreckers near you or list the item on Carpart.com.au!

To learn more about catalytic converters and other parts of your vehicle’s exhaust system, check out the blog at Carpart.com.au.

By Ray Hasbollah