What the code means

i20 means the dishwasher didn't drain properly. Frigidaire's code guide puts it as not draining completely.

Before you start

Turn the power off at the breaker, or unplug the dishwasher, before you check the hose or the filter.

If the dishwasher drains into a garbage disposer, check that the knockout plug in the disposer was removed.
Check that the drain hose isn't blocked.
Check that the drain hose isn't pinched or restricted.
Check the drain hose height. Frigidaire says at least thirty-two inches from the floor.
Check that the glass trap, the filter and the sump are clear of food.
Reset the dishwasher. Press and hold Cancel, or turn the power off at the breaker, or unplug it for three minutes.

Stop and call for service if any of these happen.

The code keeps coming back. Frigidaire's i20 page doesn't give a point to call, but its dishwasher code guide says to contact Frigidaire when an error code continues.

Source: Frigidaire: Dishwasher error code i20; Frigidaire: Dishwasher error code guide.

Based on the manufacturer's support pages. Codes can differ by model, so your model's owner's manual comes first.