Welcome to Android Central.
We need a bit more info to really try to help and not just offer you the same advice you've already gotten.
How are you connecting to the radio? Bluetooth, USB?
Do you have maps set to read out turn by turn directions? So if not connected to anything it will read out the directions? There's a speaker shaped button on the navigation screen that changes what alerts are given.
Do you get any sound through your radio from the device? Can you play music, make calls, get alerts from notifications or anything like this?
If you're using Bluetooth I'm sure at least some of the advice you're already gotten was to ensure that the BT setting for that device is set to Audio at minimum or Calls and Audio?
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Please include a brief description of what you've tried and the results if any thing changed.