johnegg Posted April 4, 2015 Share Posted April 4, 2015 see if you can get them to send you the correct one for 1/2 price? Link to comment Share on other sites More sharing options...
odycee Posted April 6, 2015 Share Posted April 6, 2015 My bet is after you replaced O2 sensors, your P0420 will come back. Link to comment Share on other sites More sharing options...
jagoulet Posted April 29, 2015 Share Posted April 29, 2015 so I believe I finally have it all sorted out. It needed a new cat. I then got a new front sensor from SubaruPartsForYou. Mileage went up by 2 mpg but PO420 stayed on. Got a new rear sensor. PO420 stayed on (despite clearing it). At that point all components were new. A check of a wiring diagram I downloaded for the specific car revealed that the sensors had been hooked up backwards by the garage that installed the cat. Easy swap as I had put anti-sieze on them. As mentioned earlier, the two sensors are the same. The connectors differ as one is triangular, one rectangular. Both connectors support 3 wires. Easy to mix up if someone was not paying attention as they are only a foot apart and the connectors are pretty much together. I now have 400 miles on the last revision. No PO420 codes. Gas mileage gained another 2 mpg. (considering the computer was working with data from exhaust after it went thru the cat, no surprise). I think I am done with it for the immediate future. Moral: details and persistance matter. Link to comment Share on other sites More sharing options...
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