Diagnosis
That's usually the washer not getting a good read on the load size. The most likely cause is a clogged or slow-filling water inlet valve.
How to Fix It
First, turn off the water supply valves behind the washer. Unplug the machine. Pull it out carefully. Disconnect the two water inlet hoses from the back of the washer. Check the small mesh screens inside the valve ports where the hoses attach. They're notorious for catching sediment. Use a flashlight to look, and pick any gunk out with needle-nose pliers or a toothpick. Reconnect the hoses, turn the water back on slowly, check for leaks, and plug it back in. Run a rinse/spin cycle with no clothes to see if it fills normally now.
If That Didn't Work
The water pressure from your house might be too low for the washer's sensors. Make sure both hot and cold supply valves are turned on all the way. Also, try running another faucet in the house while the washer is trying to fill – if that other faucet's flow is weak, you've got a house supply issue, not a washer issue.
Heads Up
When you reconnect the hoses, hand-tighten them only. Cranking them with a wrench can strip the plastic threads on the inlet valve, and that's a much more expensive repair.