A device connector receives a TCP data packet of a diagnostic device in a data TCP communication manner, encapsulates the TCP data packet into a first data packet, and transmits the first data packet to the vehicle connector through remote communication. A vehicle connector converts the first data packet into a TCP diagnostics instruction data packet and transmits the TCP diagnostics instruction data packet to a vehicle. The vehicle connector receives, based on TCP communication, a TCP diagnostics response data packet, encapsulates the TCP diagnostics response data packet into a second data packet, and transmits the second data packet to the device connector through the remote communication. The device connector converts the second data packet into the TCP diagnostics response data packet and transmits the TCP diagnostics response data packet to a diagnostic device. The diagnostic device obtains a diagnostics result and presents the diagnostics result to a user.