Cracked exhaust is common on both exhaust manifolds and manifold/catalytic converter combination. Replacing the cracked component will repair the problem.
Car Problem Reports
Honda Civic Cracked Exhaust Manifold/Catayltic Converter
Honda Civic Problem
Average Mileage: 138,083 mi (80,000 mi - 250,000 mi)
The dealer wanted my kidney in trade for the exhaust manifold. Finally, I searched the web and found a better aftermarket model with complete exhaust for less than 200 bucks.
Visitor, 1998 Honda Civic, 120,000 mi
One day my engine light turned on and instantly the engine started vibrating violently. I had the code checked and it said 02 sensor default or exhaust default. So autozone said it has to be the 02 sensor. I bought the 02, took off the heat sheild and there behold my problem it was a 2 inch crack on each side from where the 02 sensor is. Why doesnt honda cover this? I have talked to many people and have concluded, it is caused by poor part design. There is back pressure from the cat and obviously heat from the engine and when you have that combination coming down 4 pipes, (increase in pressure=increase in temp) where they meet will get very hot, they should have made that area thicker or the whole piece of better material. And they should cover this, I nor anyone with this problem caused it by any careless action, it is a defect and should be recalled.
Visitor, 2000 Honda Civic, 142,000 mi
I'm having the same issue - Check Engine light is on, giving me a P0420 code. Pulled off heat shield and have a crack almost all the way around the exhaust manifold. I'm patching it temporarily until I can get a new manifold/cat put in - thank god I'm a DIY or that could get expensive! I, too, wonder why Honda hasn't issued a recall for this problem. It's happened in plenty of their cars (over several models) and it strikes me as a poor design, and possibly even poor materials.
Visitor, 2002 Honda Civic, 80,000 mi
Found Crack in exhaust manifold / catalytic converter, I was because of Rust ! Surprised to see that Why Honda built their Cars with Cast Iron Exahaust system ? All Exhaust system in my car is rusting from engine to exhaust pipe. Dangerous gas spilled from exhaust was coming in to car cabin from A/C Fan. The replacement of exhaust manifold cost me a bill of US $800.
Visitor, 1999 Honda Civic, 136,000 mi
CEL came on on. Code P0420 called for replacement of cat.
Visitor, 1997 Honda Civic, 180,000 mi
Crack at oxygen sensor on exhaust manifold. Looking for calif. Emmisions ok replacement i can afford. Cant register since 2011'due to costs .
Visitor, 2002 Honda Civic
The crack started small and has gradually increased, currently looking for soulution
Visitor, 1999 Honda Civic, 145,700 mi
Crack behind cat converter. Loud upon acceleration. Visual diagnosis.
Visitor, 1997 Honda Civic
Had the exhaust manifold replaced.
Visitor, 1998 Honda Civic, 105,000 mi
Cracked Exhaust Mani and CC. Throaty exhaust sound coming from engine area. Replaced by muffler shop.