Code 18 is in regard to the right-side door limit switch which detects that the window is completely lowered. My interpretation of the code is that the controller turned-on the motor to lower the window but did not get feedback from the switch within a set period of time. A top opening/closing operation, will halt in the middle of the sequence without this signal.

Code 29 refers to one of the two speed signals the soft top controller uses to disable operations while the car is in motion. This code is set when it receives a signal from the speedometer but not from the ABS controller, if I recall.

By the way, in a deleted scene from the movie "Heartbreakers" Sigourney Weaver is driving an SL and Jennifer Love-Hewitt accidentally hits the top button and lowers the top while they are driving across a bridge. I watched this with a friend who had bought the DVD, and the director commented how they had specially modified the car to allow that to happen.