Exhaust gases that are emitted during the combustion process contain a lot of pollutants, including nitrogen oxides, hydrocarbons and carbon monoxide, which are very harmful to both the environment and human beings. To reduce their amount, every modern gasoline or diesel-powered vehicle comes equipped with a catalytic converter.
By design, a catalytic converter or, simply, a cat is a metal canister that sits somewhere between the engine and the muffler. Inside the cat, there are several barriers made with some precious metals, such as palladium, platinum and rhodium. When combustion gases flow through the catalytic converter, harmful gases come in contact with the metals, causing different chemical reactions, resulting in less harmful to the environment exhaust gases.
A properly functioning catalytic converter is crucial not only for the environment and humans, but also for smooth and efficient engine operation. If your cat fails, you’ll not be able to pass an emissions test as well as will experience several engine-related problems. Here are the most common of them:
Your check engine light comes on
Just about every modern vehicle comes equipped with several oxygen sensors which analyze exhaust gases. The first one that is located before the catalytic converter is called an upstream sensor, while the other one that sits just after the cat is known as a downstream sensor. Both sensors send data to the engine control unit, which compares received information to understand whether the cat does its job as it should. If both sensors provide identical readings, the computer understands that the converter doesn’t work and turns on the check engine light.
You failed a state emissions test
The government may ask you to provide trouble codes stored in your engine control unit. If there are any codes related to a bad catalytic converter, you may fail an emissions test.
Abnormal exhaust smell from the tailpipe
In a perfect world, hydrogen sulfide that is the part of the exhaust gases is converted into sulfur dioxide when the gases flow through the catalytic converter. If the cat doesn’t perform its function, you’ll notice a smell of rotten eggs.
Poor engine performance
A clogged catalytic converter will restrict the exhaust flow. This will create the force that will act against the engine, reducing its performance. If the cat gets completely blocked, the engine will stall. This usually happens due to unburnt petrol that ignites in the catalytic converter and ruins it from the inside.
Your hear a rattling noise
The catalytic converter features something similar to honeycomb inside the housing. As it ages or due to some engine problems, the honeycomb can get damaged and break off, blocking or restricting the exhaust flow to the resonator or muffler.
Catalytic converter troubleshooting and replacement
Due to its high value and price, your catalytic converter should be diagnosed and replaced by a professional. A mechanic will visually inspect the cat for damage as well as provide a backpressure test if you experience low engine performance.
A catalytic converter almost never fails on its own. Usually, its failure happens due to some problems with the engine. Thus, engine misfires can quickly ruin the catalytic converter. That’s why once you notice a flashing check engine light, you must address the problem immediately. The other typical causes of cat failures are bad fuel injectors, faulty spark plugs, worn-out ignition coils, and a leaking fuel pressure regulator. Undetected catalytic converter failures can cause damage to a new replacement unit, so all of them must be fixed before replacing is done.
Since a catalytic converter contains some precious metals, it can attract thieves who may steal the cat if the vehicle is left on the street. If this misfortune happens to you, you’ll hear a loud exhaust sound once you start the engine.