INFO ON ABS NOISE - SELF TEST NORMAL AFTER IGNITION CYCLE

Subject: ABS NOISE SELF TEST

Model and Year: 1989-91 CAPRICE 1986-91 CORVETTE 1990-91 WL VAN 1991 S/T TRUCK (4-DOOR ONLY)

All anti-lock brake systems (ABS) perform a self-test called initialization during acceleration after each ignition switch cycle.

During this test, the modulator exercises valves/solenoids/motors as the system monitors all inputs and outputs. This test is initiated at a relatively low speed so the ABS can be deactivated in the event there is an abnormal condition detected. Depending on the application, initialization occurs at different speeds, (typically between 0-8 MPH) and will vary in intensity.

As it is possible to hear and feel the initialization cycle, some customers may comment about it. Initialization is a normal condition, therefore, repair should not be attempted.

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.