Volvo FM Handbook page 38

Blocking valve
If the pressure in the braking system is too low, for
example if the truck has been parked for a long period
of time, the blocking valve must be pushed in for the
hand-operated parking brake to be released. Before the
blocking valve can be pushed in the pressure in the
braking system must be approximately 5 bar.
Instruments and controls
Caution!
Always apply the parking brake
when you leave the vehicle. If the
parking brake is not applied, a
symbol on the display will start to
flash, and at the same time an
audible warning will sound to
alert the driver.
Warning!
Check that the lever is in locked
position (position 2).
27
J0008051