Seat Belt Systems: Description and Operation

The Passive Restraint System allows the vehicle's doors to be opened without restriction by the safety belts. Without this feature, the retractor lock pendulums would lock the belts as they are pulled out of the retractors, making it difficult to open the door. The belt locking mechanism is less sensitive while the doors are being opened. Higher sensitivity is restored when the doors are closed or the vehicle is moving, enabling the belts to protect the wearer in the event of an accident.

The Passive Restraint Timer Module controls the retractor solenoid operation and signals the Multi-Function Chime (MFC) Module to turn on the FASTEN BELTS Indicator if a door is open and the Ignition Switch is in RUN. The MFC Module also turns on the indicator when the Ignition Switch is first turned to RUN regardless if a door is open or not. This is described in the WARNINGS AND ALARMS section. The FASTEN BELTS Indicator also lights to indicate that the safety belts are not able to provide full protection.

Operating a door handle or opening a door, closes the associated door latch switch. The timer module then closes its output switch and energizes the retractor solenoids for both doors. The MFC Module provides the current that powers the solenoids. A door can then be opened without interference from the safety belts.

When the door is closed, the latch switch opens and the solenoids are de-energized after about three seconds. The safety belts are now ready to protect the wearer, and the FASTEN BELTS Indicator goes out. Note that a lit indicator means that the belts may not be functional. To ensure that the solenoids are de-energized, a vehicle speed signal is also supplied to the timer module. The timer module de-energizes the solenoids any time the vehicle is moving, even if a latch switch is closed. If a latch switch fails to open and the speed signal causes the solenoids to release, the solenoids cannot be energized again until the switch opens to reset the timer module.

A shorted latch switch keeps the timer module from resetting, so the safety belts interfere with both doors opening. An open latch switch affects only the associated door. The other door still works properly.