PO420

I have a 2003 Matrix that is showing the Check Engine Light; code check by dealer [PO420] specifically points to the catalytic converter [$1833 to change!]. However, that reading shows the RANGE of the reading is "just out” of what is considered normal and upon visual inspection of the cat [these rarely go out as you guys know], shows that it is not damaged, burnt, rattling etc.

Question: This is a guess on my experiences over decades: the factory installed plugs have 107,000 miles on them. I am guessing that if I change these out, that reading should drop into the good range, since it is so close [original owner and never changed plugs] and I am betting that is the issue here; the fuel burning from never changed plugs I believe is the major cause here. WOULD MOST APPRECIATE your feedback either way; if you do not know, perhaps you could point me in a good direction, TYVM.

BTW: My heart goes out to people like you; this is like a good deed public service. I have seen on You Tube in particular, some real misinformed stuff that You Tube cannot micro manage, some of which has caused myself and others great problems.