CLUNK NOISE ON ACCELERATION AFTER A CLOSED THROTTLE. GMC Truck GMC P RV/Van/Commercial Chassis 1996

SUBJECT: CLUNK NOISE ON ACCELERATION AFTER A CLOSED THROTTLE COAST DOWN (NEW TCC CALIBRATION)

MODELS: 1996 CHEVROLET AND GMC C/K, P TRUCKS, G VAN WITH 7.4L ENGINE (VIN J - RPO L29) AND HYDRA-MATIC 4L80E TRANSMISSION (RPO MT1)

CONDITION:

SOME OWNERS MAY COMMENT ABOUT A CLUNK NOISE ON ACCELERATION AFTER A CLOSED THROTTLE COAST DOWN.

CAUSE:

DRIVELINE CLUNK IS TRANSMITTED THROUGH THE VEHICLE WITH THE TORQUE CONVERTER CLUTCH (TCC) APPLIED. THE PCM/VCM SOFTWARE CALIBRATION MAINTAINS TCC APPLICATION AT CLOSED THROTTLE. THE TCC RELEASE IS BASED ON VEHICLE SPEED AND THE BRAKE SWITCH INPUTS.

CORRECTION:

IF NORMAL DIAGNOSTICS DO NOT LEAD TO A RESOLUTION, REFLASH THE PCM/VCM WITH THE APPROPRIATE PART NUMBER LISTED BELOW. THE NEW SOFTWARE CALIBRATION WILL ALLOW THE TCC TO RELEASE AT THE CLOSED THROTTLE POSITION. THE NEW SOFTWARE CALIBRATION WILL BE AVAILABLE WITH CD ROM 1996 DISC #22 FROM GM SERVICE TECHNOLOGY GROUP.

SERVICE INFORMATION DO NOT ATTEMPT TO ORDER THE SOFTWARE/CALIBRATIONS FROM GMSPO. THEY ARE PROGRAMMED INTO THE VEHICLE'S PCM/VCM VIA A TECHLINE TOOL DEVICE.

PARTS INFORMATION NEW FILE VERSION NUMBER ----------------------------------------- 16227602 CD ROM 1996 DISC 22 16227603 CD ROM 1996 DISC 22 16227604 CD ROM 1996 DISC 22 16227605 CD ROM 1996 DISC 22

THIS NEW CALIBRATION WILL BE AVAILABLE STARTING WITH THE CD ROM 1996 DISC 22 UPDATE.

WARRANTY INFORMATION FOR VEHICLES REPAIRED UNDER WARRANTY, USE: LABOR OPERATION: J6352 OFF-CAR, J6355 ON-CAR USE PUBLISHED LABOR OPERATION TIME.

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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.