It doesn't make sense that the amp would cut off the other speakers in the car if the sub "goes out". Its possible I guess but very unlikely. The most likely possibility is that your amp is broke.

If you had access to a spare amp it would be easy enough to test.

 

My wife said she heard a pop noise from the rear of the car when the radio went out.

Is their a replacement amp (after market) other than going through the dealership?

I read where people got their 01 amp repaired but not the 2004 amp. Is there a place to get the 2004 ML amp repaired?

Thanks,
-Larry

 

I just got a reman. ML amp from lexus for $650, but you have to get give them your broken one as a core. Mine is a 2004 ls430. I was having the same issue as you described, "hear a pop and then no sound"