Yamaha BIG BEAR PROFESSIONAL 400 YFM400FPT Owner's Manual page 66

ACB-10E
Oil temperature warning
light does not come on.
Push start switch with the
transmission in neutral.
Oil temperature
warning light comes
on momentarily.
Engine oil temperature and
electrical circuit are OK. Go
ahead with riding.
Oil temperature warning light checking method
Turn the main switch to "ON" and the
engine stop switch to "
Oil temperature warning
light does not come on.
Ask a Yamaha dealer to
inspect the electrical circuit.
".
Oil temperature warning
light comes on.
Check engine oil temperature.
Oil tempera-
ture is low.
4-5
EBU00733
Oil tempera-
ture is high.
Allow to cool.