Are you talking about an FJ Cruiser? If so, page 06 08.24 of the owner's manual explains it all.
(h) Engine Oil Replacement Reminder
Light (for vehicles sold in U.S.A.)
This light acts as a reminder to replace
the engine oil.
This light will come on when the ignition
key is turned to “ON” and will go off after
about a few seconds.
When you drive for about 7200 km (4500
miles) after the engine oil replacement,
this light illuminates for about 3 seconds
and then flashes for about 12 seconds
with the ignition key turned to the “ON”
position. If you continue driving without
the engine oil replacement, and if the driving
range exceeds 8000 km (5000 miles),
the light will come on after the ignition
key is turned to the “ON” position. The
light will remain on thereafter.
If the light is flashing, we recommend that
you replace the engine oil at an early
opportunity depending on the driving and
road condition. If the light comes on, replace
it as soon as possible.
You need to reset the light after the engine
oil replacement. Reset the light by
following the procedure below:
1. Turn the ignition key to the “ACC” or
“LOCK” position with the odometer
reading shown. (For details, see
“Odometer and two trip meters” on
page 100 in this Section.)
2. Turn the ignition key to the “ON” position
while holding down the trip meter
reset knob.
Hold down the knob for at least 5 seconds.
The indicator light flashes and the
bars displayed in the odometer disappear
gradually. The odometer indicates “000000”
and the light goes off.
If the system fails to reset, the light will
remain flashing.