I have a 1994 Chevrolet S10 Blazer Tahoe 4x4 with electronic 4x4 button?

I have a 1994 Chevrolet S10 Blazer Tahoe 4x4 with electronic 4x4. When i push the 4wd button to switch to 4wd, the light switches but the 4wd won't engage until I keep hitting the button to low and high over and over. Electronic and wiring are great. Can you help me with my problem. PLEASE|||Transfer case control module. I would try pulling the TCCM fuse for a few min. If that dont work you could look at the motor that engages the front hubs. Should be on the back of the front diff.|||could b speed sensor or speed sensor has metal shavings on it from normal weer or abnormal weer