Seat Belts - Two Point Motorized Shoulder Belt Locks Up

Classification:
GI93-009

Section:
General Information

Reference:
TECHNICAL BULLETIN NTB93-133

Models:
All Models

Date:
September 12, 1993

TWO POINT MOTORIZED PASSIVE SHOULDER BELTS

APPLIED MODELS:
All with 2-point motorized shoulder belts

SERVICE INFORMATION

Some customers may complain about unwanted lock-up of two point motorized belts when exiting their vehicle.

These types of incidents are caused by stopping the vehicle quickly and opening the door when the retractor is still locked. Because the belt system is operating normally under these circumstances, replacing the retractor will not "fix" the incident. This can happen in any vehicle with two point motorized belts. Understanding how this incident happens will give customers the ability to minimize occurrences.

System Operation

The shoulder belt retractors are emergency locking retractors (ELR). This means the belt normally is not locked (free to extend) unless there is an accident or sudden stop. A pendulum type device is used to cause the belt to lock when it senses sufficient vehicle acceleration (Federal Regulations require lock-up by .7g). Hard braking or fast turns can provide enough acceleration to cause lock-up. When sufficient acceleration occurs, the belt webbing cannot be pulled from the retractor. Once the pendulum device no longer senses sufficient acceleration and a slight amount (less than .25 inch) of webbing is allow into the retractor, the belt again is allowed to extend. Note that the belt does not "tighten up", but only locks. The retraction forces of the belt are constant, only one or two pounds.

When the door is opened, the shoulder belt buckle moves forward along the track, to allow the occupant to exit the vehicle. If the shoulder belt retractor is locked at the same time, the motor may be overridden and stop along the track. Approximately 20 lbs. of force are needed to override the motor and stop the buckle movement. This may cause the occupant to feel a sensation of the belt tightening up. When this situation occurs, pressing the emergency release button on the buckle will release the belt and allow the webbing back into the retractor and unlock the retractor. The belt should always be reattached if released in this manner.

System Operation Check

To confirm that the system is operating properly, complete the following checks:

1. While the vehicle is in "Park", open and close both doors to confirm that the belts move properly along the track and remain unlocked.

2. Conduct a braking test to confirm the belts lock up properly. Forcefully apply the brakes after reaching a speed of about 15 mph. A simultaneous tug on the belt should confirm that the mechanism is functioning.

WARRANTY INFORMATION

This type of incident is caused by normal operation of the belt. Do not unnecessarily replace the belts or retractors as the incident will not be eliminated. Further replacement attempts will only result in a 397 error message and claim suspension.