Oldsmobile/Buick Repair: Service Engine Light, coolant leak, chevy venture

Question
I have a 2002 chevy venture, 3.4L 185 hp V6. My Service engine light has recently come on and I am not sure why. I tried to look under the hood for any obvious problems and anything that might look suspicious. My fluid levels seem to be fine, but when I checked my coolant it was a dark greenish color. The original color was bright green. About one year ago I had a coolant leak and had it repaired. The coolant was replaced in the reservoir and since then, has never been changed. This is the only this that seems suspicious. Can you please offer your expertise before I go into a mechanic.

Answer
Hi
I would take it to a national auto parts store (auto zone, some NAPA's, Advanced, etc..) and have the codes retreived from the computer.
ALOT of places offer this service for free. You may also check some national repair facilities (Meineke, Midas, Pepboys, Firestone, etc,\..) also.
If when you get the codes pulled, if you want to follow post back, I'll help with diagnosis, if possible.
I am sorry, I wish I could help more at this time.
I do hope this helps
Good Luck
God Bless
Pawl