Nine Signs That Your Catalytic Converter Is Clogged or Bad

It’s always important to be aware of the signs of a problem with your car so that you can get it fixed before it becomes a bigger issue.

The failure of catalytic convertors is a common occurrence. They can also be extremely expensive to replace, particularly if it's a new model.

Therefore, diagnosing a defective catalyst is crucial to ensure that you won’t replace a fully functioning catalytic converter. In this post, we’ll look at the most common bad catalytic converter symptoms, location, and function and go through what makes them so attractive to thieves.

9 Bad Catalytic Converter symptoms

A bad catalytic convert is most commonly symptomatic by a sulfur odor when your engine heats up, together with an engine check light on your dashboard.

The most common symptoms of a clogged or damaged catalytic convert are:

These aren't all symptoms that can be seen, but they are some of the most prevalent. This is a list that explains more about the symptoms to watch out for.

Verify Engine Light

The check engine light, one of the most obvious indicators of a malfunction with your car, is also one of the strongest indicators of a bad catalytic converter. It will display a trouble code relating to the catalytic converter if it is checked using an OBD compatible scanner. This must be decoded by the operator manual.

The most common trouble code when it comes to a bad catalytic converter is the P0420 code.

Acceleration Lag

If you observe delays when accelerating or a decrease in power when driving in steep areas, while all other parts like spark plugs, filters, sensors, etc. are fine, then it could be the catalytic converter that’s bad.

Many times, mechanics misdiagnose a defective catalytic convert with other components such as a bad oxygen sensor and any other sensor.

To check if your catalytic converter is clogged, keep your hand close to the exhaust pipe end and ask someone to push the accelerator pedal to increase your car’s RPM to 2000. You might have a blocked catalytic converter if you see very little exhaust coming out. If possible, compare the flow to another car.

Low or high fuel consumption

Poor catalytic converters can lead to worse or better gas mileage. A higher fuel mileage might sound appealing, but it could cause damage to your engine and lead to more costly repairs.

The improper combustion of fuel caused by clogged exhaust will cause your engine to perform less efficiently and require you to use more power. A bad catalytic convert will often result in a greater fuel consumption even though it may be possible to get lower.

You can smell sulfur.

When the catalytic converter is clogged, it will restrict the airflow of exhaust fumes so that the engine’s air-fuel mixture will get rich (too much fuel, leading to unburnt fuel)

The combustion of this excessive air-fuel mixture causes an odor smell like rotten eggs or burnt sulfur, which is an obvious indication of your catalytic converter’s malfunction.

Habitats that are discolored

If you see that the catalytic converter’s housing has turned blue or some other color, it could mean that the catalytic converter is clogged and creates excessive heat.

If your engine does not run as it should, unburnt fuel could enter the catalytic converter. The heat from the mixture causes the mixture to ignite in the catalyst and then melts the inner material. This can cause even more blockages.

Clogged catalytic converters can also cause excessive heat in the engine, which could lead to other damage. You should therefore not drive the car if the converter appears damaged.

Beginning Issues

The engine won't burn enough fuel if the catalytic converter becomes blocked. The engine will struggle to eliminate the exhaust gases because of backpressure.

Clogged converters can cause your car to start for 2-3 seconds, then stop. It is possible for your engine to shut off after 2-3 seconds of pressure building up in the exhaust.

You will see an increase in emissions

Catalytic converters can become clogged or damaged, which could cause them to stop working properly. This will cause an increment of the car engine’s emissions. It is obvious that the catalytic converter's main function is to eliminate bad emissions.

This can be seen as dark smoke from the exhaust pipes coming out of your car's exhaust system when you accelerate or idle. Your car is most likely to fail an emissions test or smog testing if it has not been inspected annually in your country or state.

Engine misfires

The catalytic convert can become clogged and restricts oxygen flow in the engines. Engines require lots of oxygen to ensure proper fuel combustion. Reduced airflow may cause overheating, due to excessive amounts of unburned fuel gases. This can also make the engine misfire.

You should have your engine fixed immediately if it isn't working properly. It can cause more costly repairs.

Rattles and other sounds

Inside the catalytic converter, there is a “honeycomb” that can get worn out and this can cause the honeycomb to break apart into pieces. You will hear a "rattling" sound coming from the catalytic convert when your engine revs.

If the car is making rattling sounds, you can have a friend press the accelerator pedal and listen to the underside.

What does a catalytic convert look like?

A catalytic converter can be found in the car's exhaust system. The catalytic converter consists of a catalyst that helps convert the car’s pollutant gases into less harmful pollutants. Catalytic converter's structure has the appearance of honeycombs.

The honeycomb shape aims to ensure that the pollutant gases flow through the more exposed surface and converts Nitrogen oxide, carbon monoxide, and hydrocarbons into safer elements like carbon dioxide . Platinum, despite being the most costly product in this category, is used to catalyze catalytic converters. Sometimes, however, platinum can be combined with palladium or rhodium in catalytic converters.

Since combustion occurs in the engine, all the burnt gases flow at about 800 degrees through the exhaust pipe, which passes through the catalytic converter, thus affecting the engine’s exhaust gas flow. A good converter can last up to 10 year. The honeycomb structure of the catalytic converter starts to suffocate slowly, which affects the engine’s performance.

What are the possible dangers to a catalytic conversion?

Catalytic converters are often getting worn with time and it most likely has to get replaced one or more times during your car’s lifetime. Some car models even have a service schedule of when it should be replaced (Even if most people don’t follow this because of the expensive replacement cost).

Wearing piston rings, clogged crankcase ventilation or other causes can cause your catalytic converter to become very corrosive. Misfires can also cause contaminants such as unburned gasoline. The honeycomb could be also damaged if coolant is allowed to enter the combustion chamber through a burst head gasket.

Catalytic Converter Theft

The precious metals found in catalytic converters include small quantities of palladium, rhodium and platinum. This metal is very appealing to thieves as scrap yards can pay good money for an old catalytic convert.

Catalytic converters are also relatively easy to steal because you just have to cut off the pipe with a tiger saw or something similar and it’s done in under 3 minutes. If you want to learn more about how to protect your catalytic converter from getting stolen you can check out our other article: How To Protect Your Car Against Catalytic Converter Theft

Locate a Catalytic Converter

Between your muffler, and the exhaust manifold is the location of the catalytic convert.

Depending on the car engine, the distance where it’s installed from the engine could differ a lot. Some engines have the catalytic convert installed on the exhaust manifold while others may install it in the middle or near the end of the exhaust pipe.

Replacing the catalytic converter

Repairing the catalytic convert can often be expensive, and it may not be worth the expense if the car is very old. There are workshops that can repair the inner honeycomb of the catalytic conversion while leaving the outside parts. This could be worth on some expensive catalytic converters, but in most cases, it’s easier and cheaper to just buy a new one.

Average catalytic converter repair costs are between $400-$2500. You can learn more about the replacement costs here: Catalytic converter replacement cost.

Most Frequently Asked Questions