The cosmic rays propagation inside the heliosphere is a very complex physical process, well described by the Parker Transport Equation (PTE). When travelling in the heliosphere, particles undergo convection, diffusion and energy changes as they move in the irregular magnetic fields originated from the Sun, and their flux is therefore modulated. The irregularities are due to the outward flowing solar wind plasma, incapsulating the interplanetary magnetic field within the heliopause. HelMod is a code developed in INFN and Università di Milano-Bicocca solving the PTE in terms of stochastic differential equations and returning the modulated energy spectrum of the particles inside the heliosphere. The extremely turbulent region from the termination shock to the heliopause – the heliosheath - is responsible for a significant part of the modulation, particularly for low energy CRs. In this work, the solar modulation for H, He, C, O, Mg and Si ions is studied in the 2000-2016 time period and compared with the Voyager 1 data, in a ~ 0.5 - 2 GV rigidity range. This procedure allows us to infer the diffusion coefficient function inside the heliosheath area, i.e. a power law with γ=1.4.