If your dishwasher is under warranty, the repair will be free or limited to the cost of a service call. A dishwasher warranty typically covers parts and labor starting from the date of purchase and lasts for 1 to 5 years, depending on the manufacturer.
Look for the manufacturer's contact information on your appliance manual or on their website. The manufacturer can often check your warranty status even if you can't find any proof of purchase and don't remember when you bought the appliance.
Using the model number, the manufacturer can tell you the manufacture date of the dishwasher and whether the appliance could still be under warranty. The model number is usually found on the inside of the dishwasher door or tub wall.