2000 Vauxhall Frontera cannot turn off 4x4

I thought mine was not turning off because the 4x4 warning light flashes constantly, I was told it was out of 4 wheel drive and the senor was playing up, on mine they tend to gunge up and corrode, case of locating/cleaning or re-newal, also I was informed when 4x4 had nt been used for a good while this could contribute, told me to drive around and keep changing back and forth for awhile to free up, I guess the code reader otherwise.. Col