My iPhone 5S will not work properly with the voice through in my 2010 Cadillac STS4 as it did before the new IOS. Now the volume drops to nothing after just a few seconds.

My iPhone 5S will not work properly with the voice through in my 2010 Cadillac STS4 as it did before the new IOS. Now the volume drops to nothing after just a few seconds. It will begin each call or each GPS direction on my Garmin app. The only time when I hear all of the conversation is when I either receive a call or initiate a call utilizing my contacts. If I utilize Siri to begin a call, it states that the call has ended.

Before the latest IOS, it worked great! This is VERY frustrating as I am a teacher and I need to be able to speak handsfree in my vehicle. Please help me with ideas of how to fix this. I have already performed a restore.

Thanks,

Steve Knote