Audio Systems: Inifiniti I 30 factory sub, nissan maxima, protection mode

Question
The factory sub in my 2001 Infiniti I 30 shuts on and off randomly while the car stereo is in operation. Sometimes it stays on for a few minutes, other times for a few seconds than cuts off. Than it will cut back on etc...Meanwhile the other speakers in the car are operating just fine. Is this a problem with the amp to the sub? I also had my battery tested and I think the voltage was like 12...is that enough to push the amp? or is it possible that I need to replace the battery in order to get enough juice to the amp? Help! Thanks...

Answer
the problem is he factory sub going bad sometimes it goes from 2 ohms to 1.ohm or less and the amplifier goes in to a protection mode
i see this problem on infinity and nissan maxima  and it is always a bad sub if getting a new sub stay with the original  not aftermarquet
good luck