Hello NickApple1,
If you're having issues with the outgoing audio, you'll want to check if the infotainment system itself has any settings to adjust the microphone level. Some vehicle manufacturers will have settings to make the microphone more or less sensitive. You'll also want to make sure that nothing is blocking the microphone in your car.
If the issue is specific to CarPlay, you can try removing the device from CarPlay, then setting it back up.
- Go to Settings > General > CarPlay.
- Select your vehicle.
- Select Forget This Car.
Then just reconnect to the CarPlay system to set the device back up. If you're using a wired connection, you can also try using a different USB cable to see if that resolved the issue.
If the microphone audio is still not working properly, you'd want to contact Apple to report that issue: Get Support
Cheers!