The paper presents a concept of an on-board diagnostic system for the assessment of vehicle state in critical situation. A vehicle state assessment is done by an analysis of given signals recorded by on-board devices. A vehicle state is described by providing its position, velocities, accelerations, rotations and also powetrain data related to engine and other vehicle parts in operation. The first prototype of this device has already been developed. It registers signals taken from inertial modules such as linear and angular accelerometers (gyroscopes) and geographical coordinates from GPS. The data from GPS together with the data from inertial modules are written into a text file and can then be visualized by geo-information software. Accelerometers will be used for detection of engine malfunctions using vibroacoustic signals analysis and for vehicle position identification and the support of GPS.