Double Traction Problem New Holland LB 115 B

Hello good someone from the forum, the workshop of a New Holland LB 115 B restrorex is that I have a problem in the double traction that is not activated in case there is someone who has knowledge in these types of problems or the workshop manual to be able to discard faults thanks.

Check the button that activates the double traction, so much that current arrives, (it checks fuses), as continuity when pressing it, then this that the election that will carry in the transmission arrives current and that this is action, the following can be a problem of low pressure at the entrance of this electrovalve, which makes not between the 4x4 (internal problem of the transmission by the transmission by leaks ..). Well, there is luck and be "little." Greetings!!