METALLIC BUZZ/RATTLE NOISE FROM INSTRUMENT. Pontiac Bonneville 1996

SUBJECT: METALLIC BUZZ/RATTLE NOISE FROM INSTRUMENT PANEL AREA WITH BRAKE PEDAL DEPRESSED (INSTALL A REVISED CHECK VALVE)

MODELS: 1995-97 BUICK LESABRE, PARK AVENUE, RIVIERA 1995-97 CADILLAC CONCOURS, DEVILLE, ELDORADO, SEVILLE 1995-96 OLDSMOBILE NINETY EIGHT 1995-97 OLDSMOBILE AURORA, EIGHTY EIGHT 1996-97 OLDSMOBILE LSS 1997 OLDSMOBILE REGENCY 1995-97 PONTIAC BONNEVILLE

CONDITION:

SOME OWNERS MAY COMMENT ON A METALLIC BUZZ OR RATTLE TYPE NOISE WHEN THE BRAKE PEDAL IS DEPRESSED. THIS NOISE MAY SEEM TO COME FROM THE INSTRUMENT PANEL CLUSTER AREA AND HAS BEEN DESCRIBED AS SOUNDING LIKE AN ABS SYSTEM SELF-TEST OR SPEEDOMETER CABLE TYPE SOUND. BRAKE PEDAL FORCE AND ENGINE LOAD MAY AFFECT THE ABILITY TO REPRODUCE THE SOUND.

CAUSE:

THE CAUSE OF THIS NOISE MAY BE THE BRAKE BOOSTER VACUUM CHECK VALVE RESONATING IN RESPONSE TO ENGINE VACUUM PULSATIONS.

CORRECTION:

A REVISED CHECK VALVE, P/N 18029764, IS AVAILABLE TO CORRECT THIS CONDITION.

DIAGNOSIS AND REPAIR BRAKE BOOSTER CHECK VALVE NOISE AS FOLLOWS:

1. DETERMINE THE BRAKE PEDAL FORCE AND ENGINE THROTTLE LOAD NEEDED TO REPRODUCE THE NOISE. ALSO, DETERMINE IF THE TRANSMISSION MUST BE IN DRIVE RANGE INSTEAD OF PARK POSITION.

IMPORTANT:

THERE IS NO POWER BRAKE ASSIST AVAILABLE WHEN THE VACUUM CHECK VALVE IS SEPARATED FROM THE BRAKE BOOSTER.

2. REMOVE THE BRAKE BOOSTER CHECK VALVE AND SEAL THE VALVE WITH TAPE TO PREVENT A VACUUM LEAK.

3. IF THE NOISE CAN ONLY BE REPRODUCED IN DRIVE RANGE, THEN BLOCK THE WHEELS TO PREVENT VEHICLE MOVEMENT.

4. ATTEMPT TO REPRODUCE THE BOOSTER CHECK VALVE NOISE. IF THE NOISE IS GONE, REPLACE THE CHECK VALVE WITH REVISED P/N 18029764. IF THE NOISE PERSISTS, THEN CHECK FOR OTHER CONDITIONS THAT CAN CAUSE THE NOISE SUCH AS GROUNDED OUT POWERTRAIN COMPONENTS.

PARTS INFORMATION:

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION NUMBER: H1240 USE PUBLISHED LABOR OPERATION TIME.

FIGURES: 00 ATTACHMENTS: 00

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.