Thread: Persistent P0420. Please help--about to hock my 05 Prix for scrap I'm so mad.

You have a high flow cat not designed to actually do anything but flow.

Get a real cat.

I went through an AC Delco direct-bolt-on cat this way, as well as a magnaflow OE equivalent cat before that. I tried everything I could without a cheater before I just got the zzp downpipe and cheated it.