Density estimates for differential equations of second order satisfying a weak Hoermander condition

We prove an extension of Hoermander's classical result on hypoelliptic second order equations, where the coefficients of the related vector fields are globally Lipschitz and satisfy the classical Hoermander condition on a dense set while the density still exists in a classical sense. Furthermore, Hoermander's classical result and related density estimates based on Malliavin calculus are recovered from an analytical point of view.