Underground self-propelled cable tool

A downhole driving unit for advancing a tool (1) in a well, comprising: a tool body (3); an electric motor (4) operating at a speed and powered by a cable (5); a plurality of extendable arm assemblies (6) connected to the tool body at a first arm end (7); a plurality of wheels (8) for contacting a wall (9) of the well, each wheel comprising a hydraulic motor (10) for rotating the wheel, each arm assembly being connected to one of the plurality of wheels at a second arm end (11); and a first hydraulic pump (12) driven by the electric motor for generating a first fluid pressure of a second fluid for extending the plurality of extendable arm assemblies, wherein the downhole driving unit further comprises a hydraulic section (15) comprising a first controllable valve (16) controlling the first fluid pressure.