You have to decide if this is a problem with the key cylinder or the linkage. If it is the cylinder, use a different key may or may not help. Open the door panel and hope you can see any linkage problems. Without open the door panel, you may be able to determine the problem by feeling. Generally, if the problem is with the key cylinder, the stop feels sharp. If it is the linkage, you should feel a soft stop. To fix a cylinder problem, you need to order a new handle from the dealer in order to match the existing key.