Navigation system unreliable
That happens. Check for updates. Unfortunately factory units are generally not reparable and require replacement. If the rest of the system works, ie radio and CD, works okay consider using your phone or a stand alone GPS.
How about explaining what you mean by unreliable. Doesn’t work all the time-gives bad directions or what?
So don’t use it. Use a more reliable app on your phone, like Waze, connected to your car’s radio with Bluetooth.