Pulling codes - having trouble

[gatorman]

I have read the instructions from many sources, many times.
When I attach my multi tester to the battery and than the the self test output, the meter reads the battery lever. I was thinking when I have been successful before, the reading was at zero. When I turn the key on, engine off, and attach the other lead, nothing happens. No sweeps.
Is it possible my computer is not working? I had to replace a few years back when the truck was running rich.
That is my problem now, my CO output is off the chart. Colorado allows 40 GPM of CO, my reading was 103.76. My CO2 is 417.89.
Am I doing something wrong or is my computer out?
I used this link: http://www.therangerstation.com/tech_library/OBD_I.html

http://www.therangerstation.com/tech_library/OBD_I.html

I also tried to purchase a tool, but checker said they don't have one.

 

[holyford86]

computers rarely ever go bad, you may have bad wiring causing the computer to not want to pull codes.