The main cat usually fails right after the pre-cat fails.  The pre-cat crumbles and clogs the main cat which restricts exhaust flow.  If you're running abnormally high (water/coolant) temps with lower boost levels, it's a good chance your main cat is no good.

We've seen a few instances where physical damaged was obvious on the main cat itself.  Contact with the road or road debris can crack the catalytic core which can lead to decreased exhaust flow.  A quick tap with a hammer on the cat body that results in the sound like rocks in a pipe means the main car has crumbled.

You can punch-out the remaining pieces of the main cat, but like the pre-cat, this will also violate emissions laws.

Unfortunately, there are not many aftermarket main cat replacements available that will last as long as the stock unit.  Most units only last a couple years.  Very high quality units are made by MindTrain and Rotary Performance.

Please check out our Pre-Cat section for more reference on the pre-catalytic convertor.

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