INFO ON ABS NOISE - SELF TEST NORMAL AFTER IGNITION CYCLE

SUBJECT: ABS NOISE SELF TEST (NORMAL AFTER IGNITION SWITCH CYCLE)

VEHICLES AFFECTED: 89-91 N, B, W, C, H, E, 86-91 'Y', 90-91 L1, M1, 91 S1, T1 4-DR ONLY

This bulletin has been revised to add the 1986-91 Y car, the 1990-91 M1 L1 Van and the 91 S1 T1 truck (four-door only). Change to the speed variation was also made.

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 and 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.