i have a 2003 s type 4.2 v8, the check engine light came on, so i scanned it and it has the po420 code, cataylst efficiency below threshold bank one. i heard you cant tell if it is the o2 sensors or the converters. so i wanna start with the cheaper part to replace first. i know there is 4 sensors but does anyone know which one or ones to replace or is it also a guess? also i found on ebay univerasal o2 sensors for the 2003 jag s type, for only $25 would these work? or do i need to pay the $200 each for the sensors at the dealership.
does anyone have a confirmed fix for this code?
here is the link for the o2 sensors http://cgi.ebay.com/ebaymotors/OXYGE...Q5fAccessories

thanks

 

anyone

 

do you have a misfire on bank 1?

 

youde do better to pull the cat for bank 1(passenger side US) and have an aftermarket cat welded in by a muffler shop, using the factory flange and pipe. Not exactly original or pretty, but you said you want cheap.