ABS System - Functional Check

91buick02

Bulletin: 91-5-6

Date: March, '91

Ref. No.: 91-128-5

Corp. Ref. No.: 115001


SUBJECT: ABS FUNCTIONAL CHECK

MODELS AFFECTED: 1991 PARK AVENUE/ULTRA AND LESABRE MODELS


All 1991 Park Avenue/Ultra and LeSabre models equipped with the Teves Mark IV antilock 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's foot is 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 upward. 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.