SERVICE MANUAL UPDATE SEC. 8A AUTOMATIC SAFETY BELTS

SUBJECT: SERVICE MANUAL UPDATE - SECTION 8A-146 AUTOMATIC SAFETY BELTS (CIRCUIT OPERATION REVISION)

VEHICLES AFFECTED: 1988-91 'W' CARS

Section 8A-146 Circuit Operation for the Automatic Safety Belts cell has been revised. Replace the existing Circuit Operation in the 1988, 1989, 1990 and 1991 W-car Service Manuals with the Circuit Operation below:

Circuit Operation

The purpose of the Passive Restraint Control Module (for 1990 Chevrolet W-car only, refers to this part as "Safety Belt Timer Module") is to allow the the car 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, when a front door is opened for entry or for exit. This would make it difficult to open the door. To overcome this difficulty, the safety belt locking mechanism is controlled by the Passive Restraint Control Module (1990 Chevrolet only Safety Belt Timer Module) which controls the operation of the safety belt retractor release solenoids.

The Passive Restraint Control Module (Chevrolet Only - Safety Belt Timer Module) receives power from the Belt Fuse. When a door handle switch is operated or a door is open, the associated Door Latch Switch will close. The Module will close its output switch and energize all the Safety Belt Retractor Release Solenoids for both doors. The door may then be opened without interference from the Safety Belts. The module will also turn on the key cylinder light to illuminate the left hand front door lock cylinder. When the door is closed the Latch Switch opens again and the solenoids are de-energized after about three seconds. The belts are now ready to protect the wearer and the key cylinder light will go out. To ensure that the solenoids are released, a vehicle speed signal is also supplied to the Module. The Module will release the solenoids any time the car 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 module.

Note: A shorted latch switch will keep the Module from resetting, so both Safety Belts will interfere with door opening. An open Latch Switch will still allow the system to operate properly when the other door is used.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.