Two years ago, I ran Lucas UCL in my 2000 Altima and got the P0420 code....low catalytic efficiency.
Stayed on for two years, with no more Lucas UCL in the tank during that time.
New engine went in last week, with a new CAT, CEL still on...ugh!!
Put 1.5 bottles of Gumout Regane HM in the 14 gallon tank two days ago, 75 miles later, no more check engine light!! PEA cleaned up the post CAT real good, real quick. First time in two years the light has been off.