I have 2002 Sienna XLE van. I got engine check code P0420 which says "Catalyst system Efficiency below threshold (Bank 1)." So, I bought CATACLEAN from Amazon. I have already mixed this cleaner liquid when gas tank is about 1/4th full and poured 12 oz. of liquid. Drove the van for 15 minutes before I filled up gas tank. I have repeated this for 2 times and 3rd time is going on. But I don't see engine check light going off and it is still on. What should I do? Please advise. Thanks.