USB port for this device only used for charging, it can provide maximum output to 5V/2.5A. Don't use high-power electrical equipment or power inverter in order to avoid damage. When searching phone in Bluetooth mode, please make sure the phone within the normal range and Bluetooth in the pairing mode
In the status of inserting TF card/U disk, TF card/U disk will be in priority play status, if you want to connect Bluetooth, then you need to adjust the play mode. When the device in FM transmitter, don't turn on the high volume (generally 25 or less position) in order to avoid sound distortion, adjust the volume using the car stereo adjustments.
The machine FM transmitter built-in antenna, while also should try to avoid using strong local radio frequency signals to get better sound quality. Due to various differences in the phone itself, the method used in the Bluetooth may be different in practice. After power on, some mobile phones may not support automatic connection, so they need to connect by hand.