INFO. ON THE 1996 4L80-E TRANSMISSIONPRODUCT. Chevrolet Tahoe

SUBJECT: INFORMATION ON 1996 4L80-E TRANSMISSION PRODUCT UPDATES

MODELS: 1996 CHEVROLET AND GMC C/K, G, P MODELS WITH HYDRA-MATIC 4L80-E AUTOMATIC TRANSMISSION (RPO MT1)

THE FOLLOWING PRODUCT UPDATES HAVE BEEN IMPLEMENTED ON THE HYDRA-MATIC 4L80-E TRANSMISSION DURING THE 1996 MODEL YEAR AND HAVE AN EFFECT ON SERVICE:

UPDATE DESCRIPTION ON-BOARD DIAGNOSTICS (OBD) II SOFTWARE (CALIBRATION): NEW SOFTWARE WAS CREATED FOR OBD II DIAGNOSTICS. WHEN MOST DTC'S ARE SET, THE LINE PRESSURE "DEFAULTS" TO MAXIMUM LINE PRESSURE. SOME DTC'S WILL DEFAULT THE TRANSMISSION TO 2ND GEAR ONLY. REFER TO SECTION 7A-17A OF THE APPROPRIATE SERVICE MANUAL FOR MORE INFORMATION ON DTC DIAGNOSIS.

DETENT DOWNSHIFT ENHANCEMENT (CALIBRATION): THE DETENT SHIFT SPEEDS HAVE INCREASED TO TAKE ADVANTAGE OF THE IMPROVED ENGINE HORSEPOWER AND TORQUE. TO REDUCE SHIFT BUSYNESS, THE TRANSMISSION WILL MAINTAIN THE DETENT MODE LONGER AND WILL NOT UPSHIFT UNTIL THE THROTTLE POSITION IS REDUCED TO APPROXIMATELY: 65% (L29); 75% (L31); 70% (L35); 83% (L56 AND L65).

TCC SHIFT ENHANCEMENT-L29 + L31 HD ONLY (CALIBRATION): THE TORQUE CONVERTER CLUTCH (TCC) WILL REMAIN ENGAGED OR WILL BE APPLIED IN 2ND, 3RD AND 4TH GEARS DURING HIGH THROTTLE POSITIONS. THIS IMPROVES EFFICIENCY OF THE TORQUE CONVERTER AND TAKES ADVANTAGE OF THE IMPROVED ENGINE HORSEPOWER AND TORQUE AT THE HIGHER ENGINE RPM. THE TCC IS NOT RELEASED ON CLOSED THROTTLE DECELERATION. THE TCC RELEASE IS BASED ON VEHICLE SPEED AND BRAKE SWITCH INPUTS.

MANUAL SECOND DOWNSHIFT ENHANCEMENT (CALIBRATION): MANUAL SECOND IS INHIBITED AT HIGH VEHICLE SPEEDS. IF MANUAL SECOND IS SELECTED AT A HIGH VEHICLE SPEED, THE TRANSMISSION WILL DOWNSHIFT IN A 4-3-2 SEQUENCE AS THE VEHICLE SPEED DECREASES.

TORQUE MANAGEMENT ADDED TO 4.3L (L35) (CALIBRATION): TORQUE MANAGEMENT ENHANCES SHIFT FEEL QUALITY BY CONTROLLING ENGINE TORQUE OUTPUT DURING THE UPSHIFT.

1-2 SHIFT ENHANCEMENT PACKAGE: NEW 1-2 ACCUMULATOR PISTON, ACCUMULATOR PISTON CUSHION SPRING, CUSHION SPRING ADDED TO THE INTERMEDIATE CLUTCH NEW THINNER INTERMEDIATE CLUTCH PLATES, AND COMPUTER SOFTWARE CHANGES TO COMPLEMENT THE HARDWARE CHANGES.

QUICK CONNECT COOLER FITTINGS AT THE TRANSMISSION (SOME MODELS).

REVISED PRESSURE REGULATOR VALVE, NEW LOW AND REVERSE BAND MATERIAL, NEW FINISH ON THE REACTION DRUM.

CAST POST AND NEW SPRING FOR THE PARKING PAWL.

OVER-MOLDED DESIGN SPEED SENSOR.

OUTPUT SPEED SENSOR PLUG ON 4WD VEHICLES.

NEW LOW ROLLER CLUTCH.

UPDATE IDENTIFICATION THE PRODUCT UPDATES WERE IMPLEMENTED INTO PRODUCTION ON ALL 1996 4L80-E MODELS AT S.O.P.

EFFECT ON SERVICE THE PARTS LISTED ABOVE WILL ONLY SERVICE 1996 MODELS, EXCEPT FOR THE SPEED SENSOR AND THE OUTPUT SPEED SENSOR PLUG ON 4WD VEHICLES. THE SPEED SENSOR WILL SERVICE ALL 1991 THROUGH 1996 MODELS. THE OUTPUT SPEED SENSOR PLUG WILL SERVICE 1994 THROUGH 1996 4WD MODELS. REFER TO THE GMSPO CATALOG FOR THE CORRECT PART NUMBERS OF THESE PARTS.

FIGURES: 0 ATTACHMENTS: 0

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.