ABS FUNCTIONAL CHECK AT 6 MPH LIGHT HUM & PULSE NORMAL

SUBJECT: ABS FUNCTIONAL CHECK ON 1991 DE VILLES AND FLEETWOODS

All 1991 DeVilles and Fleetwoods equipped with the Teves Mark IV anti-lock brake system utilize a functional check during normal operation. The functional check is required because the ABS system is a stand-alone type and is only activated during potential lock-up conditions.

During the functional check the EBCM commands the ABS pump on for a half second after the vehicle reaches a speed of six mph. The EBCM checks for ABS pump operation by monitoring the ABS pump run sensor inputs. This check is performed to ensure proper operation. The functional check is done once during an ignition cycle and only when the brakes are not applied.

If the driver has their foot on the brake pedal, but not enough to activate the brake lights (less than .8 inch), the ABS pump check will occur at six mph and the driver may feel the brake pedal pulsate and gently push back on their foot. A light hum from the ABS pump may also be heard by the driver during this check.

Both the pulsation and the hum are normal conditions and in no way signify a problem with the ABS system. During a normal acceleration the functional check is invisible to most drivers. Still, it is possible that some owners may comment on this condition.

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.