What does a catalytic converter do?

If you don’t want to fail your MOT, then you need to know what your catalytic converter does and how it works.


Part of the emissions control system of your vehicle, the cat, as it’s often known, helps to convert harmful gases into harmless compounds.
 
The first cats were built in the 1950s by Frenchman, Eugene Houdry. Initially for use with smoke stacks, they crossed over into vehicle manufacturing when pollution became a concern in the 1970s.
 

What does a cat converter do?

Your cat is located in your exhaust system. It treats the following gases, turning them into harmless carbon dioxide, nitrogen and steam:
  • Hydrocarbons in the form of unburned petrol
  • Carbon monoxide which is formed when petrol combusts
  • Nitrogen oxides created by the heat of the engine
 
The gases pass over a honeycomb or catalyst of metal coated ceramic. Palladium, platinum or rhodium are the most commonly used precious metals - this is the component that makes a new cat so expensive. The catalyst is then housed in a muffler style package on your vehicle’s exhaust.
 
Once in place, a series of complex chemical reactions occur that help to neutralise harmful components, creating lower emissions.
 

How your catalytic converter is tested

There are several tests that your local garage can perform to see whether your cat is performing properly or whether it’s likely to fail the MOT.
  • Emissions test: your garage should have the latest technology to be able to conduct an accurate emissions test to check that your cat is functioning properly
  • Temperature check: the rear of a properly functioning cat is much hotter than the front, so your garage will use a temperature check to assess how well it’s functioning.
  • Pressure check: your garage should also measure the back pressure to assess whether there are any blockages
  • Rattle test: this simple but effective test measures whether the honeycomb is still intact. Wait until the cat is cool then give a rap with your fist. Any rattling means you have a problem.
 

MOT due soon, or, are you unsure? 

Use our MOT Checker to find out when your vehicle is due its annual MOT. Once you know, book your MOT with your local Protyre garage today.

MOT Checker     Book MOT
 

Why did your catalytic converter fail?

If your cat fails in testing, it’s important to know why, so you can avoid making the same mistakes. This is an expensive component to replace, so the more knowledge you have, the fewer mistakes you’ll make.
 
Using leaded fuel or failing to check your fuel injectors can allow your cat to become blocked and fouled. Failed or faulty oxygen or MAP sensors can allow too rich a mixture to poison the cat. Misfires and bump starts can also allow unburnt fuel to damage and eventually destroy the cat.
 

Getting your cat converter checked

At Protyre, we’re the local garage you can trust, so when we check your cat, you know you’re getting the best possible service and the most accurate assessment. Why not book a free exhaust check before your annual service and MOT? That way you can have your car MOT tested with the peace of mind that your cat is working to the best of its ability.

Book Free Exhaust Check

About the author

Dean Richardson

Dean is a Regional Director for Protyre who is also responsible for the running of our Protech Academy. The ...

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