If the OBD port does not have power, then the code reader can not read it. If the OBD port has power and the code reader powers up but can not read anything then the PCM is dead or the fuse powering it is blown.

my OBD2 port had no power, and nither did my power port on dash, i couldnt find the problem so i had ta wire it ta another spot with a fuse so i didnt burn it up LOL, u might have the same problem, run a hot wire with a fuse link the the power wire ta ur power port and then see if it will read

well i fixed it, it was the plug for the glow plugs and injectors in the valve cover..