CES light doesnt always come on during bulb check

[70stroker]

Guys I bought this 96 tahoe OBD-II truck a few weeks ago. When I got it the Check Engine Soon light came on during the bulb check just fine. Now that i am a little more familar with it im noticing little things (like i figured i would) Nothing major just little things. One thing that is bother me is this light, sometimes when you turn the key to ignition and all the bulbs come on in the dash this light will come one, other times it wont, So i know its not a bulb. I have never seen a vehicle do this.

Any ideas?

Thanks

 

[SunlitComet]

either a loose connection or your pcm is deuced.