Thank You for writing into AskPatty!! To address your concern, this is a great website; http://auto.howstuffworks.com/question4821.htm (to help understand the function, and fault patterns.
In some cases, you can replace your O2 sensors (oxygen sensors) and this will remedy the check engine light. Catalytic converters faults often are caused from a misfire or other serious engine problems. You can always seek a second opinion.
Here is another great webpage for reference
Hope this helps!
A. J. Valle
Steve, the most common repair for a 2002 Subaru Legacy is “replace catalytic converter,” at an average cost of $1,100. You can see other common repairs for your car at www.carmd.com/snapshot. That doesn't mean you should run right out and replace it, but if a trusted mechanic is telling you it needs to be done, it's probably accurate. You can get a second opinion from an ASE-certified technician or from a product such as CarMD, but don't wait too long. A failed catalytic converter can quickly cause engine damage if ignored too long, as indicated by a blinking check engine light. If you see a blinking light, pull over immediately, stop driving and have the vehicle towed to a trusted repair shop. Note that a catalytic converter normally won’t fail unless a smaller faulty part, such as a spark plug or O2 sensor, is ignored for too long. Paying attention to your car’s warning signs -- even when the car seems to be running fine -- and fixing little problems early can help you avoid expensive catalytic converter repairs, among others. Best of luck to you! Kristin Brocoff, CarMD.com Corp.
〉 Answered on Nov 29th, 2011 by Kristin Brocoff, Director of Corporate Communications at CarMD.com
First of all you need to know what caused the Cat to go bad. Replacing it is probably only half the answer. Usually it fails because raw gas is being dumped into it from a bad injector and it burns in the Cat causing damage. If this isn't fixed, then you'll have another bad Cat.
Check out this website:
Usually you see high fuel consumption and no change in acceleration when you press the gas. I would get a second opinion. Also, check your warranty...exhaust components are usually covered longer than the body warranty. Good luck.
〉 Answered on Nov 29th, 2011 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines