have you replaced the pcm on this vehicle by any chance, if you did, the replacement pcm will not communicate with the old/original immobilizer, you have to replace the immobilizer as well to gain communication again. btw today i tried a 2001 mitsubishi montero and there was no immobilizer special function at all for this vehicle, only code read, erase and data that is it. i had to used the mut3. anyway as i was saying back to your issue. if you did not replace the pcm/ecu make sure all voltage and ground are present at your immobilizer and pcm, you will need to be looking at a wiring diagram. 2 questions is your sel light on and is the security light coming on?. also i had to used a new immo on mine, was not able to program a used one.