My rear speakers have never worked since i bought the car. Last week my front speakers stopped working and now only the rear sub works. I pulled the amp out and am using this pic as a reference:
https://www.clublexus.com/forums/3558924-post7.html

When I pull the "B" jack out, the front speakers work and the rear sub doesn't. When I put the "B" jack back in, the front speakers don't work and the rear sub does.

Is this an amp issue?

THanks!

 

Yes thats what happened to mine, and I have the exact year you have. Replace the amp (I found a used one on ebay) and you should be in business. Or if you want, now you have a good excuse to upgrade your entire system.