Not really a "pre-tensioner" like the newer cars have. From what Im looking at of the diagram is that the seatbelt tension reducers are probably on when the door is open. Time control unit is what controls the time the seat belt light flashes ect. If you goto the EL section look under time control it may give you some better idea. Not sure what triggers the tension reducer but I would assume that it works of the signal from the door switch so the seatbelt release and you can open the door easier.