Car is fully operational except for convertible top which is closed on car and will not open. Pulling switch E137 (or convenience opening with key) starts the top opening cycle successfully. Door glasses are lowered several inches, the convertible top lock is unlocked and top opens several inches, and the electric motor on hydraulic pump in the trunk can be heard humming. However, the cycle abruptly stops. Pushing switch E137 causes the convertible top to lower back to fully closed position and re-locks. I plan to check the level of fluid in the hydraulic unit, which is difficult to access (behind driver's seat in luggage compared, hidden under lining). Any other suggestions would be welcomed.