Hey out there. My 97 Chevy Express 2500 'service engine soon' light appeared yesterday at start up in the morning. When I went to O'Reilly's to read the code it said "NOT CONNECTED". So we tried another reader and had the same result. Three weeks ago I changed plugs, wires, cap and rotor. Other than that no other changes recently. I notice no difference in how the engine is running, and it definitely runs better after the recent tune up I did. Also, I had just filled up the tank the night before this happened. So my question is how do I go about finding out what has caused the light to come on? Is there a chance the reader and the computer are not "connected" some how? Any help is appreciated as I am towing my son's car from Tulsa to Florida for school in 3 days!!