The invention provides a system for monitoring a vehicle that includes a wireless appliance in electrical contact with an in-vehicle computer. The wireless appliance features: 1) a data-collection component that supports communication software that collects diagnostic data from the computer; and 2) a data-transmission component, in electrical communication with the data-collection electronics, configured to transmit an outgoing data packet comprising the diagnostic data over a network and receive over the same network an incoming data packet that modifies the communication software. The wireless appliance communicates with a host computer system that is configured to: 1) receive the outgoing data packet from the network; 2) process the outgoing data packet to generate a set of vehicle diagnostic data; 3) host a web site on the Internet that displays the vehicle diagnostic data; and 4) send out the incoming data packet over the same network to modify the communication software.