I have a 99 SOW with 105K miles. This past weekend the CEL came on and I took it to the dealer. They say they pulled code P0420 (Cat efficiency below threshold bank 1), and told me I need to "replace catalytic converters and possibly both sensors and hardware."
I've done some reading on this topic and I have a few questions that I hope someone could answer. First off, I'm a bit uneasy about the vageness of the diagnose. It sounds like they're not sure whether it's a bad cat, a bad sensor, or a bad gasket. I don't want to pay $1200 for the job if all that's really necessary is an exhaust gasket or a new O2 sensor.
Is it normal that both cats go bad and need replacement at the same time? How easy and expensive would be to just replace the sensors and the gaskets as a first step? Does the P0420 code really mean "bad cat, must replace" or is it just an indication of different readings between the 2 sensors (which may or may not be due to a bad cat)?
Any suggestions on how I should proceed?
Thanks in advance,
- Manuel.