Hi all,

My wife's 2000 Blazer wants some of my attention now. Last week it threw the P0420 code. I have a '99 S/T shop manual and I was looking at the diagnostic chart and I came upon step five: install scan tool, clear codes, run truck until DTC sets, run diagnostic. I don't have a Tech 2 with that capability. How else do I test the truck when I get to that step of the diagnostic tree?

I haven't done any diagnosis yet other than just pulling the code. I have to check the first things first like ignition parts, MAF sensor, exhaust leaks, etc. I'm a little surprised there isn't a P030x code; it seems to me that if there's a misfire or other ignition problem causing the P0420 there should be some kind of P030x code. I do know that the truck doesn't have an AC Delco cap and rotor. I put the factory spec AC Delco plugs in it back in August, gapped to .060, IIRC. Other than that the cap, rotor and wires are all off-brand.

If anyone else has suggestions I'm happy to read them!

 

PO420 is Catalysis efficiency. usually means the cats about to go.