Toyota Coaster 2015 Owner's Manual page 51

If the indicator or buzzer comes on...
(h)
(indicator and buzzer)
(i)
(j)
(indicator and buzzer)
(k)
(l)
(indicator and buzzer)
(m)
(n)
Low vacuum warning buzzer
44
Drain water.
Take vehicle to Toyota dealer.
Perform manual regeneration.
Take vehicle to Toyota dealer.
When engine switch is "ON", close emergency door but keep it unlocked and close
door lever cover.
Close passengers' door.
Stop and check.
Do this.