Dead ECU?

I have a 99 cherokee. I have a CEL on. I hooked up my code reader and it reads no codes, it is capable to read live streaming data but sees no data. I know it is not the code reader as I hooked it to second 99 cherokee and it reads everything fine. Does this mean the ECU is toast?

I found the problem. There was enough corrosion on the vehicle plug to prevent a good contact. I little clean up with a wire brush and success. Thanks to all who replied.