Hello Mhalpert10,
Thanks for reaching out to the Apple Support Communities. We understand you are experiencing some issues with adjusting the volume on your iPhone while it is connected to your vehicle. We are happy to help provide some guidance.
To begin, how are you connecting your iPhone to your vehicle? Are you using a USB cord or connecting it via Bluetooth? Does your car support CarPlay?
Normally, you would adjust the volume either using the side volume buttons on the iPhone, or using the volume slider within the Control Center or Settings on your iPhone. Take a look at the steps listed in the following article to try adjusting the volume slider in Settings:
Adjust the volume on iPhone
If the issue continues, let us know the answers to the following questions so we can get a better understanding.
- Are you able to adjust the volume of your iPhone when it is not connected to your car?
- Have you been able to adjust the volume while connected to your car in the past?
- When did you first notice this become an issue? Was it after any sort of update or change to your iPhone or car?
Keep us updated on how it goes.
Cheers.