I'm getting the same 420 code with my PM. The service history looks like it had the heads redone at around 90-something thousand miles - it's now at 108k. Based on the comments here, I'm wondering if that caused it to throw the code. The shady dealer that I bought it from probably cleared the code, so I didn't see it until I drove it around for a while.
There were several open recalls with the PM that I had the dealer close out, and while I was at it, I asked him to replace the O2 sensor while they were in there. I can't remember exactly what they said, but I think he said they ought to replace either the whole exhaust or just the cat and the two sensors in the 1st bank. He did mention that the cat might be shot as others have noted that if it was running rich, it'll destroy the cats. In either case, they quoted me something like $800-900 for the repair and almost fell over.
I did end up getting it to pass emissions inspection as-is by clearing the codes with my scanner, running some Techron through the tank driven about 100 miles. It gave me some unhappy message in the report but ultimately passed. I still have another year until I have to take it again, but I'm wondering if there's any harm in driving it as-is? Is there any chance it'll eventually go on and destroy the second cat?
There were several open recalls with the PM that I had the dealer close out, and while I was at it, I asked him to replace the O2 sensor while they were in there. I can't remember exactly what they said, but I think he said they ought to replace either the whole exhaust or just the cat and the two sensors in the 1st bank. He did mention that the cat might be shot as others have noted that if it was running rich, it'll destroy the cats. In either case, they quoted me something like $800-900 for the repair and almost fell over.
I did end up getting it to pass emissions inspection as-is by clearing the codes with my scanner, running some Techron through the tank driven about 100 miles. It gave me some unhappy message in the report but ultimately passed. I still have another year until I have to take it again, but I'm wondering if there's any harm in driving it as-is? Is there any chance it'll eventually go on and destroy the second cat?
