Got the P0420 code, took straight to Muffler shop, and they read the code, and replaced the converter.. This has happened three other times.. This time the car only had 2000 miles since the last one was replaced in July.. I have checked oil, looks fine, and was just changed.. Not losing coolant, checked coil packs, air filters.. new plugs and wires about a year ago.. I never get any other codes.... The converters are always under warranty, but I would like to know what is causing the converters to go bad.. Yes it is an aftermarket... I am going to replace upstream O2 sensor tomorrow. Another thing. My wife drives this car to and from work about 3 miles round trip, and in the city.. Probably never gets over 50mph at any time.. Wonder if that is causing the converter not to get hot enough... Any thoughts much appreciated....

 

cheap cats have low cerium content...which is the oxygen storing element of the cat. If it can't store 02 it will set a p0420. If you pre cat 02 cross-counts are switching at the proper rate; you may need to buy a quality cat.

 

Going to recheck for coolant leaks, etc.. The muffler shop said it is running rich, alot of black stuff, but I never get any other codes... Thanks, may have to get a oem replacement cat, I am sure they are tired of replacing it under warranty..

 

What kind of car? What engine size? You need to provide more info. Most likely junk cats. We only use oem cats as we have seen a high failure rat of aftermarket.

 

2003 Chevy Malibu 3.1 LS.. 123,000 miles.... Oil looks fine, and not losing coolant that I know of.... Am going to look at better tomorrow, and check intake gaskets