To keep it simple, Blueooth 2.x or 3.x adapters are not supported by Apple iOS because iOS only supports selected Bluetooth profiles. The serial profile from an ELM327 Bluetooth 2.x/3.x scanner is not supported. Android devices support more Bluetooth profiles.
OBD2 Bluetooth Adapters that are compatible with iOS are Bluetooth 4.0 / Bluetooth LE (Low Energy) adapters, such as:
Apple iOS Bluetooth support is divided into four categories:
- Standard devices - These are automatically supported by the system. The specific protocols are described in the following AppleCare article http://support.apple.com/kb/HT3647
- Bluetooth LE - These are accessible via the Core Bluetooth framework
- iOS-to-iOS Bluetooth networking
- MFi - Other devices must go through the MFi program