Welcome Gary
.
Changing the main cat will not fix the P0420 code. P0420 is Bank 1 (firewall side) Precat, and P0430 is Bank 2 (radiator side) Precat.
Yes, I would suggest that you try the Berryman B12 first. If it doesn't help, then the mileliminators ($30 from
www.mileliminators.com) will be the way to go. With the mileliminators, the PCM will not turn on the CEL for P0420 and P0430 codes. Note that other codes not related to the precats may still be stored.
As for emissions, if is is a code check (they just plug in the and check for codes), then you should be good with the mileliminators.
If it is a tailpipe sniff test, unless the precats and main cat are in really bad shape, it should still pass emissions test. In the off chance that it fails the sniff test, then you should try changing the main cat (which is much cheaper than the precats). Note that you will need mileliminators or they will fail the car due to the visual CEL being on.
My experience with the installation of Mileliminators
1) Drive up Rhino ramps ($40 at Advance).
2) Disconnect battery negative terminal.
3) Went under and unplugged connectors and then unscrewed both BOTTOM O2 sensors (22mm or 7/8 inch crescent wrench $7. You can buy a O2 sensor socket if you want, $12 at Advance).
4) In the comfort of kitchen table, splice (wire splice connectors $3) the mileliminators to the O2 sensor wires (clear and explicit instructions come with the mileliminators). Tape connection well with duct tape (water in connectors will give you P0136 or P0156 CEL codes).
5) Reinstall O2 sensors to vehicle.
6) Reconnect negative terminal battery
Took me about 1 hour 15 minutes. Vehicle might run rough for a day or so until PCM goes through the OBD II drive cycle again.
