Toyota 2011 Prius Owner's Manual page 543

Follow the correction procedures.
After taking the specified steps to correct the suspected problem,
check that the warning message turns off.
Warning message
(U.S.A. only)
(U.S.A. only)
PRIUS_U (OM47685U) DVD
5-2. Steps to take in an emergency
Details
Indicates that the engine oil is
scheduled to be changed.
A buzzer also sounds.
Comes on approximately 4500
miles (7200 km) after the
engine oil is changed. (The
indicator will not work properly
unless the oil maintenance
data has been reset).
Indicates that the engine oil
should be changed.
A buzzer also sounds.
Comes on approximately 5000
miles (8000 km) after the
engine oil is changed (and the
oil maintenance data has been
reset).
Correction
procedure
Check the engine
oil, and change if
necessary.
Check and change
the engine oil.
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