From the 2009 OU Passover Guide:
Leave the dishwasher unused for twenty-four hours,
make sure that the dishwasher is clean, and then run
two cycles. If the lining of the dishwasher is plastic,
it is debatable as to whether one may kasher it; ask
your Rabbi for guidance.
If it’s kosher enough for the OU, it’s kosher enough for me!