Since the check engine light turns on for many different reasons, use an OBD code scanner to scan your vehicle for the problem. Catalytic converter issues usually have an error starting with P0420 or P0430. [3] X Research source
Rattling could also be a sign that parts of your exhaust system are loose and need to be tightened.
As your catalytic converter gets in worse shape, your engine will lose more and more power. \
The broken material in your catalytic converter can cause a misfire when it blocks the exhaust, but it may fall out while driving. When it gets jostled back into your exhaust again, then it makes your engine stall.
Exhaust can also be a sign that there’s a problem with the engine heating up too much, which damages the catalytic converter over time. Changing your oil can help keep the engine running smoothly.
Take your vehicle to a mechanic so they can tell you what needs to be fixed so you can pass the emissions test.
