Toyota PRIUS Manual page 472

4-3. Do-it-yourself maintenance
NOTICE
 If you remove the air cleaner filter
Driving with the air cleaner filter removed may cause excessive engine wear
due to dirt in the air.
 If the brake fluid level is low or high
It is normal for the brake fluid level to go down slightly as the brake pads
wear or when the fluid level in the accumulator is high.
If the reservoir needs frequent refilling, it may indicate a serious problem.
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