Just discovered mocking is hardly possible with Windows Phone 7 - skipping it for now..

Renamed the OBDDeviceCommunicator class to OBDDeviceCommunicatorSync, so there's room for the async version now, too.
Extracted two classes (ResponseEventArgs, OBDSensorDataEventArgs) into new files
Async methods implemented. Solution isn't ideal yet, but it compiles at least :-) Next on: Redesigning the data structures such that the difference between 'SensorAvailability'and 'PIDSensor' disappears - after all, an 'availability' sensor is still a sensor.
Changed PIDCode system to a more flexible structure

The structure is a tree-structure from now on.