A characteristic feature of internal combustion engines of a vehicle used in real operating conditions are frequent changes of the values of power in the powertrain. The analysis of the results of the road test through a measurement of parameters of engine (CAN BUS) in a passenger car proves, that the changes of parameters and engine power are frequent. Particularly under the conditions of urban test-drive their frequency, range and dynamics is significant. As a result the engine speed, throttle opening and fuel consumption are not constant, as in the case of measurements realized under stationary conditions on an engine test stand, while determining of the engine speed characteristic. The paper presents the analysis of the engine parameters determined based on on-road tests rather than laboratory tests.