intermittent check engine light

the check engine light on my 01 chevy blazer has been coming on and off for the past week....i have noticed that it stays on for about 13 -15 miles then goes off for no set number of milesjust comes on whenever... the mileage on my blazer is at about 49,200, i was wondering if anyone out there could tell me if this is something to do with a computer proggram that lets you know that your coming up on your 50000 mile services or what else it could possibly be... has anyone heard of this problem before... just wondering before i go out and pay to have it checked.... thanks

Bring it to a Garage, and have them hook it up to the computer.

I had that happening on my 96. It turned out to be two of my O2 sensors...

GM does not turn check engine lights on at mileage intervals. The light comes on because there is a problem.