I bought a car that is more than 10 years old with a renewed certificate of entitlement (COE). On the first inspection, I was told that the "cat" was missing and that I had to install it, and have the car re-tested. What is "cat" and why do I need it when my car is running with no problems?

This is not a rare situation. Some car owners remove the "cat" - catalytic converter - from the exhaust system to improve performance and to avoid the cost of replacing a clogged converter.

A catalytic converter is an emissions-control device. It looks a little like an exhaust muffler and houses expensive natural elements, which chemically treat exhaust gases to reduce noxious pollutants.

Removing the cat converter means that the car is no longer in compliance with the emission standards which it was originally imported with.

You can detect a car without a cat easily. The exhaust gas has a distinctive and strong smell.

So while your car runs smoothly, it is polluting the environment a lot more than an equivalent model with a cat converter. You are thus required by law to reinstall it.

Shreejit Changaroth