P0420 - Cat. below efficiency threshold: Bank 1.
2000 Legacy OBW LTD.
I have a 2000 Legacy OBW Ltd. with 61K on the clock. My car is BONE STOCK as far as the engine is concerned. I got a P0420 "Cat. below efficiency threshold: bank 1". I was told by the AutoZone clerk that this is an O2 sensor going bad and I needed to replace the sensor. I have since been told by McDade and HndaTch627 that this is really my cat going bad. Updates to come.
*Update* OK I have to fess up to being dumb. I had replaced the spark plugs before I got the code and I had used Bosch Platinum regular plugs, not the "plus 2 or 4" gimicks just regular platinum plugs. I know that I had been warned about using Bosch plugs but they were the only things available at the time. I ended up calling the stealer (Southern States) and talking to Quincy the lead Suby mechanic. I told him that I had done the 60K service and he said "You put Bosch Platinum plugs in it didn't you.". I told him I had and he told me to get them out and replace them with NGKs. I was able to find regular copper NGK "V-power" plugs that crossed to the original Champion plugs. Once I put the plugs in and drove it a couple of days the light went out but I still had it cleared by AutoZone. I have been driving it now for about a week in the fixed state with no light and much better fuel economy.
/kicks self in butt/