Originally Posted by MDTAHOE

You need to replace the converter 99% of the time the cat is bad. The code po430 does not say anything about o2 sensor. The correct code definition is catalyst efficiency below threshold bank 2. How many miles are on the truck. The converters are covered under the federal emissions warranty 8 years or 80,000 miles. It is mandated by the federal government the dealer can not refuse unless you have modified the exhaust or the engine.

Originally Posted by 500k miles

anyone who says stuff like this should not be trusted to start with gm actually states that code can be caused by a faulty 02 code along with a list of other options I worked for a gm dealer and in three years I seen I cat on a 5.3 get replaced and it was misdiagnosed from this code and it was just an 02 sensor