i have a 99 jeep GC and when i go above 15 Mphs my check engine lights comes on but when i turn the jeep off and turn it back on the lights goes off, my engine is an 4.0 inline 6

 

We don't have crystal ***** that will tell us what is wrong with a Jeep a thousand miles away. You need to have the codes pulled with a scan tool.

 

I have no code, when I turn the Jeep off and start it back up the light goes off until iv reach 15mphs

 

Even if the light goes off, if it's been on long enough it will set a code. It may not show as a key code, but it should come up with a code reader, maybe just as a "pending" fault. I have a P0740 (torque converter solenoid) code come up about once a month regardless of how I drive it. If this solenoid was really shot, it would set every time I went fast enough for the clutch to set. This code HAS to be reset with a reader/scanner.