The exhaust system has three main functions:

• Safely get hot exhaust gas from the engine out the tailpipe
• Treat the exhaust to remove harmful pollutants
• Muffle the engine noise

Exhaust gas is poisonous. You don't want it getting into the passenger compartment. For example, carbon monoxide can be deadly. That's why you should never run your engine in a closed garage. If you have a leak in the exhaust system, exhaust could get into the passenger cabin and make you sick or even kill you.

If you smell exhaust in the vehicle, roll down your windows and get it inspected. You may smell or see exhaust coming from the engine compartment or under the vehicle if you have a leak. Sometimes the sound from an exhaust leak is loud and obvious. Sometimes it's a ticking sound when you start the engine that goes away as you drive. That could be a small crack or a bad fitting that leaks when it's cold but seals up when the metal heats and expands.

Now, let's address the environmental issues for our Chula Vista community. Exhaust gas contains a number of pollutants and particulates. The catalytic converter scrubs some of those harmful substances. And diesel vehicles have systems to deal with soot.

Catalytic converters eventually wear out and need to be replaced. They're expensive so you want to help them last as long as possible by keeping the fuel system clean and replacing your air filter. These components need to be tested for proper functioning with an emissions test from time to time.

And that leaves the muffler. The beauty of getting a new muffler is that you can suit your taste: Some want whisper quiet and others like a little rumble. And some like a roar when they drive down our Chula Vista streets.