Carplay volume decreases after sending text / GPS directions.

If CarPlay doesn't detect your iPhone, make sure CarPlay isn't restricted. Go to Settings > Screen Time > Content & Privacy Restrictions. If Content & Privacy Restrictions are turned on, tap Allowed Apps and make sure CarPlay is enabled. Go to Settings > General > CarPlay, tap your car, and then tap Forget This Car.

If you need help with CarPlay - Apple Support (IN)

Search for accessories that have completed MFi certification. Once an accessory has completed MFi certification requirements and is reported to Apple as sold/distributed, it will be searchable in our public database of authorized Lightning, headset, charging, iAP-enabled, and Find My network-enabled accessories.

Learn how to identify counterfeit or uncertified Lightning-based accessories.

On your device, go to Settings > Bluetooth and turn on Bluetooth. Stay on this screen until you've completed the steps to pair your accessory.

Pair a third-party Bluetooth accessory with your iPhone or ...

If you're still having trouble with your car's audio system using CarPlay or Bluetooth, try the Aux cable. To get it fixed, there are two options:

1. Take your car to a reputable car dealer or car audio specialist. They have experienced technicians who can diagnose the problem with the Aux cable. This could be a loose connection, a faulty cable itself, or an issue with the system's Aux port. They'll be able to repair the issue or recommend a replacement cable if needed.
2. Consult your car's infotainment system manuals. These manuals often include troubleshooting sections that might address common Aux cable problems. You might find instructions for resetting the system, cleaning the Aux port, or confirming the cable's compatibility.

Before taking your car to a dealer, it's always a good idea to check the manuals first. This can sometimes save you time and money if it's a simple fix you can handle yourself. However, if the manuals don't offer a solution, or you're uncomfortable tinkering with the system, then a car audio specialist is the way to go.

Refer to the list of cars that are compatible with CarPlay --> iOS - CarPlay - Available Models