hey there
when i got my es 300 i had a chek engine light caming up and trac off light to, p0420 code
the previous owner change full exausht systeme
but they put a litle flow catalyzer( speling in english??), like the one for the corralla or camry 4cinlinder and it was to much restriction
i put a Hi Flow catalyt systeme and no more trouble
rem