You'll want to be sure the Launch from car setting is enabled on your LG. Here are steps to check if this is enabled:
Tap the Profile tab
Tap the Settings gear in the upper right corner.
Under Bluetooth for devices make sure there is a check next to Launch from car.
Please note, enabling the launch from car setting will prompt a notification from Pandora that will appear any time you connect to any Bluetooth device, since Pandora cannot distinguish between vehicles and other Bluetooth devices. This notification is required by your Android device. If the message bothers you, you'll then need to disable the Launch from car setting.
Use your mobile device only when conditions allow and as permitted by applicable law.