Addendum to last post:
Soooo I went to Autozone to get my parts for my tune-up and I just changed my spark plugs. When I turned the ignition to fire it up "POOF"... no more check engine light. The code 420 was gone!
I'm going to continue with the rest of my tune-up but Cherokee, I think you are right when you said that it may have been preset to go off at a certain milestone.
2007 Jeep Compass Sport 4WD - Black
4 Cyl, 2.4L CVT
215/65R17 - Continental ProContact ECOPlus
Replaced entire front end suspension at 190,000mi (control arms, inner/outer tie rods, bushings, etc.) (did it myself)
new Monroe struts at 160,000/mi (did it myself)
Ball Joints 2x-both sides - various mileage (did it myself)