hydrallics in tailgate door

Your Honda is covered for 3 years or 36,000 miles for defects in manufacturing. Some items are covered for longer and you can find out by looking in your owners manual or calling your local Honda dealer. If it is a failed part due to a manufacturing defect and withing the time and mileage restrictions it's covered under Honda's warranty. I'll assume that this is a manual rear hatch and that there has been no tampering or accident damage to the vehicle. When the rear hatch won't stay open it's because the pressure in the tailgate supports has diminished. Replacing the supports will take care of the issue.