Volvo FM Handbook page 156

6 Engage the differential lock between the front
wheels.
The control lamp on the instrument panel will come
on.
7 Release the clutch pedal
8 Drive away from the slippery area
9 Release the accelerator
10 Disengage the differential lock
The differential lock between the front wheels will be
disengaged if the differential lock between the rear
axles, the differential lock between the wheels on the
rear axles or the front-wheel drive is disengaged.
Engage the differential lock just before reaching the
slippery surface and disengage it once you have past
the slippery surface.
None of the wheels may be spinning before the
differential lock is engaged!
1 Make sure none of the wheels are spinning
2 Depress the clutch pedal
3 Engage the differential lock between the rear wheels.
The control lamp on the instrument panel will flash.
Driving 145
Warning!
Drive carefully once the
differential lock is engaged.
Never turn corners on firm
ground with the differential lock
engaged.
Note!
The differential lock is not engaged
until the warning lamp on the
instrument panel flashes. The
differential lock is engaged as long
as the warning lamp is flashing,
even if the switch is turned off.
J4015830
J4015831