SES code reading problems

Hi all, I have a real head-scratcher here. 99 S10 4X4 around 120K miles 6 cyl (of course), 5-speed manual tranny. I bought the truck used about 5 years ago so I don't know all of its history. Its always had this quirk of jerking, misfiring, running rough when I try to maintain highway speeds, it normally wears off once the truck gets warmed up, never has lit up the SES light. But recently the SES light finally lit during one of the episodes. I took it to Autozone to have them read the codes and their computer wouldn't even power up off my truck. Any suggestions??

Hi all, I have a real head-scratcher here. 99 S10 4X4 around 120K miles 6 cyl (of course), 5-speed manual tranny. I bought the truck used about 5 years ago so I don't know all of its history. Its always had this quirk of jerking, misfiring, running rough when I try to maintain highway speeds, it normally wears off once the truck gets warmed up, never has lit up the SES light. But recently the SES light finally lit during one of the episodes. I took it to Autozone to have them read the codes and their computer wouldn't even power up off my truck. Any suggestions??

Check all fuses.
The diagnostic connector provides ground and 12 volt power to the scanner.
If no power or ground the scanner will not power up.

http://www.troublecodes.net/OBD2/

I had the same trouble with my 96 S10 6cyl. I read in one of the other posts to try and replace the cap and rotor with parts from a dealership and my truck seems to be running pretty good for the past 3 days.