Yamaha F13.5A Owner's Manual page 24

Basic components
The buzzer will sound (if equipped on the
G
tiller handle, remote control box, or main
switch panel).
If the warning system has activated, stop the
engine as soon as it is safe to do so. Check
the oil level and add oil as needed. If the oil
level is correct and the warning device does
not switch off, consult your Yamaha dealer.
ECM00100
CAUTION:
Do not continue to run the engine if the
low oil pressure warning indicator is on.
Serious engine damage could occur.
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ZMU02081
ZMU02360