K 1500 Truck 4WD V6-262 4.3L (1991)
PROM - Programmable Read Only Memory: All Technical Service Bulletins
A/T - Delayed Shifts in Low Gear in 4X4 Mode
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.
