Toyota Prius 2011 Manual page 560

5-2. Steps to take in an emergency
STEP 5
Have the vehicle checked at nearest Toyota dealer as soon as possi-
ble.
Overheating
■
The following symptoms may occur when your vehicle is overheating:
●
Hybrid system output decrease.
●
Steam is coming from under the hood.
560
If necessary, add power control
unit coolant up to the full line.
Water can be used in an emer-
gency measure if power control
unit coolant is unavailable. 
(P. 572)