Yes, in some cases cleaning the catalytic converter with a fuel system cleaner might temporarily clear the P0420 code if the problem is caused by dirty injectors or another part of the fuel system. However if the problem is caused by a faulty oxygen sensor or a blocked catalytic converter then a cleaner won’y fix the problem. If there are other codes such as P0166 and P0167 present then it’s likely that a faulty oxygen sensor is to blame.