I have a 2000 Toyota sienna and its throwing a code for catalyst efficiency below threshold bank 1?

Question

What should I do to fix this problem?

Answer 1

Catalytic below threshold Bank 1

You have P0420, this will require a catalytic replacement, The fix is to prevent another catalytic that is installed to degrade rapidly, the engine management should be inspected, if  sparkplug are worn a tune will be required.