Siri Navigation Voice Over Car Speakers during Sirius XM/AM/FM - Solved!!!
I have an iphone 6s with version 11.4.1.
And my new car is a Subaru Forester 2.5i Premium "without navigation," which I still have yet to understand fully what that means. But I digress . . .
Today I was able to finally solve my inability to hear Siri's navigation instructions cut in over my car speakers whenever I was listening to Sirius XM!!! I got a critical clue from an Apple forum post . . . one critical puzzle piece that was missing was that I didn't yet have the "Allow HFP Prompts" slider button selected to "ON" because Apple's default is apparently the "OFF" position. HFP stands for Hands Free Profile.
The other critical puzzle piece was: Just because you don't see an "Allow HFP Prompts" slider button on your phone when you're sitting at home out of your car, you might still very likely get this option to magically appear once you're in your car with your phone! In other words, there's truly hope if you don't see the Allow HFP Prompts slider, even greyed out while you're sitting at home!
These steps worked for me. These instructions are for an iphone 6s and the Apple Maps app; dunno about Androids or other iphones or Google Maps, hopefully there's something similar....
Perhaps some steps below are overkill, but some combo of them worked . . .
1. Be in your car, out of your garage, with your phone.
2. Have your car running. No idea if this is necessary, but it helps, since you'll be testing while driving very soon anyway.
3. If your car has a Bluetooth setting as a source setting (from the steering wheel button or car screen), set it to Bluetooth. Dunno if this matters, but doing this didn't hurt my results.
4. Press the Maps icon.
5. Do whatever it takes to enter an address to navigate to... ideally an address you're familiar with so you'll know if you're getting navigation instructions when you expect them.
6. Press Go.
7. Swoop up from the horizontal line about 1/2 inch from the bottom of the screen, NOT from the very bottom of the screen; the very bottom seems to result in a different display.
The resulting display should include an "Audio" icon.
8. Press the icon that says "Audio." I literally saw the word "Audio" in my Apple Maps app, not just a speakerphone looking icon.
9. The resulting display should include "Normal" and "Loud" voice. "Normal" is good, since hopefully you'll get the voice working just fine... Normal should be loud enough I think. At first you will NOT see any "Allow HFP Prompts" slider to appear below the voice volume settings!
10. Wait for it . . . maybe there's some sort of Syncing going on . . . then an "Allow HFP Prompts" slidebar magically appears below the voice volume settings!
11. Slide to the ON position (green).
12. Turn your source or whatever the setting on your car is that will give you Sirius XM (or perhaps AM or FM, haven't tried those yet).
13. Drive excitedly, trying not to crash in your excitement to hear Siri cut in while listening to Sirius XM, AM, or FM!!!
Hope this helps!