A portable controller device having an OBD-II port interface and a microcontroller that interacts with a vehicle network through the interface, including programming for querying successively the vehicle network for one or more parameter, and for retrieving values for the parameter returned from the network. The retrieving values for the parameter returned from the network is compared with an inferring response or parameter value, such as an absence of a response to query of the monitoring parameter, that if satisfied can infer that the journey status of the vehicle has changed from ‘underway’ to ‘ended’, and identifies the monitoring parameter as a candidate parameter. The journey status can be confirm as ‘ended’ when successive querying of the candidate parameter returns the same an absence of a response.