Usually the linkage doesn't work due to neglect and lack of previous use. A fair bit of lubrication helps, combined with some gentle force.
Diff lock can be engaged independently, which will be indicated by an icon on the dash (if done successfully). It may take some distance of driving until it comes on. Your vehicles doesn't have a 4WD-light (only diff lock warning) as it features permanent four-wheel-drive.
Johannes
There are people who spend all weekend cleaning the car.
And there are people who drive Discovery.
Bookmarks