HELP!PLEASE, P0420 Code!

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

ricky g

New Member
Jun 26, 2014
Reaction score
Hey everyone, brand new to this, thanks in advance for any help. Have a 2000 Yukon, 4.8L. Awesome vehicle, bought it brand new in 2000, wanted the cargo doors instead of the tailgate so had to special order it. It has 242K miles on it and it looks and runs like the day I picked it up from the dealer. No rough idle, no sputtering, no loss of power, just really ****ty gas mileage. Anyway, problem is I can't pass smog because of a P0420 code. My scanner shows all tests complete except for EVAP and SECONDARY AIR. However, I've been reading that a P0420 code is a catalytic convertor code??? My scanner tells me the CATALYST test is complete with no error codes so I'm really frikken confused. My cheap ass scanner only reads codes, can't see the 02 sensor voltage. Maybe I need to get a better scanner but damn, $100 bucks, might need that for a part. Could it be that right after the CATALYST test it dropped the P0420 and the EVAP and SECONDARY AIR tests are just not finished yet? Or did the CATALYST test complete with no error and it moved on to the very next test which was SECONDARY AIR and that's when the code was dropped? Anyone out there have a suggestion? I'd really appreciate it! Thanks!
Last edited: