Hmdi input has lost audio

Remove you sat nav from the car (I am presuming it is not factory fitted) attach to your computer via a USB cable there will probably be a USB mini or micro socket on the sat nav, you should have been supplied with the correct USB cable when you bought the unit.
Once you have connected your unit to the computer go to the sat nav manufacturer website and select products. Go to your product and look for downloads or updates.
Also check that the sat nav screen isn't asking you questions to communicate to your computer. Sometimes you have to agree that the unit an talk to the computer or nothing will happen.
When you have found the relevant update save it to your sat nav unit being carefully not to unplug the USB lead untill you are completely finished.
When you restart your sat nav it should be up to date.

The HDMI inputs are on the back upper left of the unit. the 4 on the left are INPUTS (like you connect you DVD to port 1) then you need a 2nd HDMI cable from the white 5th port going OUT to your TV HMDI port.
http://www.pioneerelectronics.com/StaticFiles/PUSA/images/Product%20images/Home/VSX-523_back.jpg

Fault with main board. Damaged component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. http://electronicshelponline.blogspot.com/ . In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.

You need to do the input assign. The receiver needs to be told which physical sockets are assigned to what buttons. Once you assign the inputs, then press the corresponding input button. So if you assign HDMI 1 to be your Satellite receiver on the TV/Sat button, then you'll get the sound

Power lost on two units in one car is a little unique. Does it lose power in the middle of a trip or when you first get into car? I would recommend bench testing to direct 12v unit to see if car is causing voltage loss.

What kind of signal are you using for the cable/sat? Most receivers cannot use a digital input (optical, hmdi) to output a signal to zone 2. You may have to make an analog connection to get it to work.

Change the HMDI cable, might fix the problem, intermittents of this type are very difficult to trouble shoot.

Hello,
What you need to do is connect the HDMI from your source(SAT, Cable box or DVD) directly to your tv. Then, connect audio from that same source down to your pioneer receiver.
Good Luck

may have to go into radio menu to turn on aux input.or xm/sat radio input.

It sounds very much like your receiver needs repair by Sony.
www.esupport.sony.com