My stereo in a 2004 Nissan Sentra has no sound. All of the buttons and controls work, but therer is no sound.

https://www.modifiedlife.com/2006-nissan-sentra-car-stereo-wiring-guide/

the 2004 sentra
correct not listed as
Swirl control valve position sensor online
none on ebay etc
if no other nissan vehicle part listing
to suit the sentra

possibly discontinued part
might need to source a used one from a wrecker

P1137 2004 Nissan Sentra Description Swirl control valve position sensor is installed on the intake manifold.
The sensor is connected to the front end of the valve shaft of the swirl control valve.
The sensor responds to the valve shaft movement. This sensor is a kind of potentiometer which transforms the swirl control valve position into output voltage, and emits the voltage signal to the Engine Control Module (ECM).

Read more: http://www.autocodes.com/p1137_2004_nissan_sentra.html

Fit a new stereo ,

open trunk and look very carefully at the copper colored wires on bottom of rear speakers and make sure they are not contacting speaker frames and shorting out.often occurs whe stuffing large items in trunk.this will shut down all four channels so radio is not damaged.hope this helped.

same this happned to me in my 2006 sentra. the volume for the radio is gone. i can tune, its just barely audible/ quiet. weirdly though it sounds perfect when playing CDs. i almost thought maybe it got switched in to mute mode or something. did you figure out your problem?

Battery MUST be tested to be SURE OF IT after that Go to Starter, Solidoid is Part of the Starter and Is Normal to Replace as a PAIR

if you are putting an after marker stereo the wiring is different from a stock radio some audio stores sell adapters for after market stereos that you jus clip on to stock wiring

easiest way to see if the left outputs have gone is to swap the right and left speakers over. if the left works out of the right channels you know if the set has had it.hope this helps

I have the same car...04 nissan sentra....with the exact same problem....left side speakers just quit working. I still do not know what caused the problem, or how to fix it. I know it not the wiring, it is a defect within the stereo.

can you hear this through the stereo?  If so you may have a problem created somewhere in your ignition , where the stereo is picking up a fluctuating signal.