A/T - Delayed Shifts in Low Gear in 4X4 Mode

9216chevy12

Number: 91-386-7A

Section: 7A

Date: AUGUST 1991

Corporate Bulletin No.: 177116


Subject:
DELAYED SHIFTS IN LOW GEAR - FOUR WHEEL DRIVE MODE


Model and Year:
1991 K2/K3, V2/V3 TRUCKS WITH 4L80-E/4L80-EHD AUTOMATIC TRANSMISSION


TRANSMISSION APPLICATIONS: SUBJECT:

1991 HYDRA-MATIC 4L80-E/4L80-EHD (MT1) DELAYED SHIFTS
IN LOW GEAR - FOUR WHEEL DRIVE MODE (NEW MEM-CAL/PROM)

TRANSMISSION MODELS: VEHICLE APPLICATIONS:

ACP, BJP, CKP, DLP K AND V TRUCKS
(FOUR WHEEL DRIVE VEHICLES)


Service Information:

Some HYDRA-MATIC 4L80-E/4L80-EHD Transmissions may experience delayed shifts and malfunction code 85 generated when four wheel drive low gear is selected. This condition is caused by the PCM/TCM selecting the output speed sensor located on the transfer case instead of the output speed sensor from the transmission. Malfunction code 24 will not set if the output speed sensor from DRA (Transfer) is selected.

A new MEM-CAL/PROM is released for K and V trucks.

Figure 1:

Date of Production Change: (Figure 1)

Starting January 15, 1991 (Julian Date 015), all ACP, BJP, CKP, and DLP transmission model applications were built with a new MEM-CAL/PROM.

Service Procedure:

Refer to Section 7A of your Service Manual for Output Speed Sensor check for four wheel drive.

To correct this condition, a new service calibration MEM-CAL/PROM should be installed for all four wheel drive vehicles.


Service Parts Information:

Body Engine/RPO Current PCM/TCM New MEM-CAL/PROM

K 4.3L LB4 16154381 16161422
K 5.7L LO5 16154421 16161192
K 5.7L LO5 16154431 16161196
K 5.7L LO5 16154441 16161201
K 5.7L LO5 16154451 16161205
V 5.7L LO5 16154461 16161217
V 5.7L LO5 16154471 16161433
K/V 6.2L LL4 16161529 16161710
K 7.4L L19 16154241 16161151
K 7.4L L19 16154251 16161156
K 7.4L L19 16154261 16161166
K 7.4L L19 16154291 16161173
K 7.4L L19 16158731 16161178
V 7.4L L19 16154311 16161183
V 7.4L L19 16154331 16161187
V 7.4L L19 16158741 16161225
V 7.4L L19 16154361 16161230
K 7.4L L19 16154271 16161427

Parts are currently available from GMSPO.

Service Manual Reference:

Refer to the On-Vehicle Service Manual Section of the appropriate service manual for proper replacement procedures.