Catalytic converters (sometimes called "cats") are emission-prevention devices which degrade over time and require replacement. While the location of the catalytic converter varies based upon which model Mazda you have, the general procedure to replace one is the same: You will need to gain access underneath the car and unbolt the the cat from its location in the exhaust system.
Park your Mazda on flat ground and engage the parking brake. Use a hydraulic jack to raise the front end of the car, placing it on jack stands.
Locate the catalytic converter. Follow the exhaust system from the engine toward the back of the car. The catalytic converter will typically be located immediately after the factory header underneath and slightly behind the engine. Look for an oval-shaped canister with two oxygen sensors connected at the front and back of the catalytic converter housing.
Spray the bolts that connect the catalytic converter to the exhaust system with penetrating oil. There will be two bolts on each end of the housing. You must spray them liberally and repeatedly. Ideally, you will spray the bolts several times in the hours preceding removal. Rust and age will make the cat bolts extremely tight, and if you attempt to remove them without penetrating oil, there is a high chance the bolts will snap.
Use the oxygen sensor socket and ratchet to remove the oxygen sensors. Handle them carefully and not damage the sensors once removed. You can zip tie them out of the way.
Use a socket and ratchet to remove the bolts from the front and rear of the catalytic converter. You may want to use a breaker bar to apply additional leverage as these bolts will be very tight. Remove and dispose of the old catalytic converter and the old gaskets.
Insert the new catalytic converter into the factory location, using new exhaust gaskets which will have been included in the kit. Reinstall the bolts both front and rear, and then reinstall the oxygen sensors. Lower the vehicle off the jack stands using your hydraulic jack.
