Toyota 2003 Prius Owner's Manual page 167

Service reminder indicators and warning buzzers48.
If the indicator or buzzer comes on...
or
(a)
(indicator and buzzer)
(b)
(indicator and buzzer)
(c)
(d)
(e)
(f)
(g)
92
If parking brake is off, stop immediately and contact Toyota dealer.
Fasten driver's seat belt.
Fasten front passenger's seat belt.
Take vehicle to Toyota dealer.
Take vehicle to Toyota dealer.
See multi–information display.
Drive without hard acceleration.
Do this.