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Check your Owner's manual. Most likely your differential fluid is
shared with the transmission so there would be no separate drain.
How often to change?
Best answer: "As needed."
Look at new transmission fluid.
Look at the fluid on your transmission dipstick and compare.
If they look nearly the same you're fine.
If the fluid is discolored or smells burned you'll need to change it a
several times.
Drain and fill. Drive for some period of time and repeat.
The automatic transmission still has a clutch like a standard or
manual stick shift.
The difference is, there are multiple plates of friction material and
they are actuated automatically with hydraulic pressure.
Wear particles from the friction disks gets in the lubricating fluid -
the oil which lubricates the gears.
The gears are "planetary" gears that are continuously engaged. This is
different from a standard transmission.
Still the primary cause of failed automatic transmissions is neglected
fluid changes.
So, as always, clean oil is cheap insurance against a far more costly
repair later.
Be sure to check the final level with the transmission at normal
operating temperature. You'll need to drive the car normally for at
least ten miles.