Cracked exhaust is common on both exhaust manifolds and manifold/catalytic converter combination. Replacing the cracked component will repair the problem.Google+
Car Problem Reports
Honda Civic Cracked Exhaust Manifold/Catayltic Converter
Honda Civic Problem
Average Mileage: 144,904 mi (40,000 mi - 334,000 mi)
Visitor, 1998 Honda Civic, 136,000 mi
I started my car up and started driving and 30 seconds on the road the engine started shaking strangely, it was very startling, and my CEL light popped up. Turns out my manifold cracked then and there or cracked just enough to throw things out of rhythm. So I searched online for recalls and it turns out the honda civics from 97 and a few years before had the same cracking problem and Honda was taken to court resulting in recalls. But after that the 98 manifolds cracked too. So I went to Honda dealership and they would not help me. The representative said, "There is no recall on the '98 and as far as Im concerned it must be a rare problem because I haven't heard of 98's cracking on the manifold." With my response, "just because every 98 civic with a crack has not drove into your dealership and reported you the problem DOES NOT MEAN the problem with your companies manifolds does not exist!" She shrugs her shoulders, it was going no where. I believe if us 1998 honda civic owners make our problem known that practically all manifolds are cracking we can too fight for a replacement manifold! Honda likes to keep things on the hush, look at the 2002-2005 civics, majority of their transmissions are going out around the 100,000 mark nearly after warranty expires, no recall on that either. Power to the people!
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, 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, 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, 1999 Honda Civic, 136,000 mi
CEL came on on. Code P0420 called for replacement of cat.
Visitor, 1999 Honda Civic, 100,000 mi
engine light on and can smell exhaust fumes
Visitor, 2005 Honda Civic, 95,000 mi
badly cracked exhaust manifold
Visitor, 1997 Honda Civic, 123,000 mi
Cracked exhaust manifold from O2 sensor going down the length about 4 inches
My sister noticed the problem because i'm hard of hearing i have no idea when it really happened