'98 S-10 ALDL stopped working

I have a '98 S-10 and had the "service engine soon" light come on. (Not the first time it has.) Have a CEN-TECh OBD ll Code Reader to use on it. Always worked before, but the last time I put it on the truck it didn't. Tried it on a Dodge Dakota and it worked. Went back to my truck with it, and nothing. So, I'm not sure if unhooking the battery for awhile works or not, but it didn't work. The (CEL) check engine light never even goes out (After battery reset and restarting).
Anyone have any thoughts on this?
Hope I explained it right.

At the data link connector, pin 16 is voltage, hot all the time, cigar fuse. Pins 4 and 5 are grounds. Check voltage and ground.

After you do that you need to check the diagnostic circuit. You may have a short to ground between the CEL light and PCM.

At the data link connector, pin 16 is voltage, hot all the time, cigar fuse. Pins 4 and 5 are grounds. Check voltage and ground.
Sorry I haven't got back with you on this. Been very busy.
I need to know how the pins are numbered to do this check.