Results of detailed investigations of the conductivity and Hall effect in gated single quantum well GaAs/InGaAs/GaAs heterostructures with two-dimensional electron gas Eire presented. A successive analysis of the data has shown that the conductivity is diffusive for kFl = 25-2.5. The absolute value of the quantum corrections for kFl = 2.5 at low temperature is not small, e. g., it is about 70 % of the Drude conductivity at T = 0.46 K. For kFl < 2.5 the conductivity looks like diffusive one. The temperature and magnetic field dependences axe qualitatively described within the framework of the self-consistent theory by Vollhardt and Wölfle. The interference correction is therewith close in magnitude to the Drude conductivity so that the conductivity σ becomes significantly less than e2/h. We conclude that the temperature and magnetic field dependences of conductivity in the whole studied kFl range are due to changes of quantum corrections and that transition to hopping conductivity occurs at lower conductivity value.