Had check engine light come on and scan shows po 420 code. What is this ?

Catalytic converter failure. something else may be causing this to appear. You need to confirm no other codes exist and run a full diagnostic for correct results. Catalytic converters are designed to last the life of the vehicle.

http://www.autocodes.com/p0420_ford.html View the entire page... Look at possible causes and testing instructions.

Probably the catalytic converter.....Have a 2002 Ford Escape....had to replace catalytic at about 120,000 miles.....they don't last the life of the vehicle.