How do i know if my 2003 kia sedona van is a 16 volt or 24 volt engine

All modern vehicles are 12 volt systems. The cover over your engine is how many valves the engine has. 16 valve or 24 valve, 16 valve would be a 4cyl and a 24 valve would be a 6 cyl.

Your engine should be a 3.5 liter 6 cyl

Ghost do yourself a big favor. Do lots of homework, ask lots of questions, get a WRITTEN warranty on any purchase of major components that you purchase. Slow and steady. Remember, advice here is free. No one has any reason not to give you the straight scoop.