As stated above you'll need a code reader, personally I would tell the wife I need the superchips or hypertech and not say a damned thing about a scanner. If you do opt for a scanner you can pick one up from auto zone or the likes it just has to be an OBD III reader I do believe.
HD Diesel Mechanic
00 Durango 5.9L SLT
I've got a few things done
I haven't had the check engine light on in a long time but I know if you hold the trip/reset button while you turn the key to the "on" position and then let go it will test all the gauges. I don't know if it will tell you what the code is. I always use a snap-on scanner.
Prime Performance 5.9 bored .030 over,HER1828AL Cam,HPHD-MAG1-SP Heads with 110 Springs,Crane 1.6 Roller Rockers,Ported Intake,Holley 52MM Throttle Body,MSD 24/lb Injectors,MSD Ignition,Hughes Engines Re-flashed ECU,Gibson SS Headers,etc.