INFO ON NEW TRANS. CALIBRATIONS. Chevrolet Astro

SUBJECT: INFORMATION ON NEW TRANSMISSION CALIBRATIONS

MODELS: 1998 CHEVROLET CAMARO 1998 PONTIAC FIREBIRD

1998 CHEVROLET AND GMC G-VAN AND C/K, M/L, S/T MODELS 1998 OLDSMOBILE BRAVADA 1998 HOLDEN COMMADORE WITH HYDRA-MATIC 4L60-E TRANSMISSION (RPO M30)

ALL 1998 LIGHT DUTY TRUCKS AND V-6 F-CARS EQUIPPED WITH 4L60-E RECEIVED A NEW TRANSMISSION CALIBRATION CALLED ELECTRONICALLY CONTROLLED CAPACITY CLUTCH, COMMONLY REFERRED TO AS "EC-CUBED." THIS REVISED CALIBRATION WILL PARTIALLY APPLY THE TORQUE CONVERTER CLUTCH (TCC) AT A LOWER VEHICLE SPEED THAN PAST CALIBRATIONS AND AT A CONTROLLED SLIP RATE. THIS REVISED CALIBRATION IS INTENDED TO INCREASE FUEL ECONOMY AND REDUCE NVH (NOISE VIBRATION HARSHNESS).

ONE FEATURE OF EC-CUBED THAT CUSTOMERS ARE MOST LIKELY TO NOTICE IS INCREASED ENGINE BRAKING ON A CLOSED THROTTLE DECEL WHILE IN 4TH GEAR. PRIOR TO EC-CUBED, THE TCC WAS RELEASED WHENEVER THE THROTTLE WENT TO ZERO SO IN 4TH GEAR THE VEHICLE HAD VERY LITTLE ENGINE BRAKING. ON AN EC-CUBED VEHICLE, THE TCC WILL STAY LOCKED AT ZERO THROTTLE UNTIL THE BRAKE IS APPLIED AND 4TH GEAR ENGINE BRAKING WILL BE NOTED. EC-CUBED IS APPLIED WHEN ENGINE TORQUE IS BELOW 200 FOOT POUNDS, ABOVE 200 FOOT POUNDS TCC IS LOCKED-UP.

THE AMOUNT OF ENGINE BRAKING WILL VARY DEPENDING ON ENGINE AND VEHICLE SPEED AND GENERALLY IS LESS THAN THAT EXPERIENCED ON A COMPARABLE VEHICLE EQUIPPED WITH A MANUAL TRANSMISSION. ALSO, LITTLE OR NO ENGINE BRAKING WILL OCCUR UNTIL THE ENGINE GOES INTO DECEL FUEL CUTOFF. THE AMOUNT OF TIME NEEDED TO ENTER DECEL FUEL CUTOFF WILL DEPEND ON ENGINE OPERATING PARAMETERS AND CALIBRATION.

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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.