ftrms

This morning i was dropping my baby off at daycare and the cel came on i checked it real quick and it wad 67 catalyst system below threshold... i dont even know what that is or how to fix it, if anyone can help me out its much appreciated.

car 99 civic ex
stock besides header and intake and cam gear

itsnotfast

Cat might be clogged.

ftrms

how can you tell if its clogged? i replaced the cat about 4k miles ago

itsnotfast

Then it shouldn't be clogged unless your motor is dumping oil or coolant into the exhaust.
o2 sensor possibly?

ftrms

I replaced the one by the cat when i replaced the cat, but not the one on the header, what is the code anyway?