16NA019

Bulletin No.:
Service Bulletin
Date:
16-NA-019
November, 2019
INFORMATION
Subject:
Information on Transmission Adaptive Functions and Correcting Low Mileage Harsh
Shifts, Slips, or Flares
Brand:
Model:
Model Year:
from
VIN:
to
from
to
Engine:
Transmission:
All
Equipped with
8L90 and 8L45
Automatic
Transmission
(RPOs M5U,
M5T,
M5N, M5X)
Buick
Cadillac
Chevrolet
GMC
GM
Passenger
Cars and
Trucks
2016
2018
Involved Region or Country
North America, N.A. Export Regions
Condition
Some customers may comment on low mileage vehicles with an automatic transmission
that the shifting may feel too firm (harsh), slips, or flares. Customers should be advised
that the transmission makes use of an adaptive function that will help to refine the shift
feel while driving and improve shift quality.
Correction
Important: Using Tis2Web, please check the ECM/
TCM Software/Calibrations against what’s currently in
the vehicle and if the description of the update is
relevant to the customer concern, please perform the
update prior to proceeding with the learns below. By
completing the software/calibration update, the clutch
adapts will clear and thus a Service Fast Learn followed
by Adaptive Learning may be needed to further learn
specific clutches if shift concern exists.
The following should be used to determine what steps
should be followed within this document. The 8-Speed
transmission utilizes a total of 5 clutches to obtain all
the ratios. Utilize the chart within this document to
determine which clutch may require additional adaptive
learning.
• If a transmission replacement was required, reset
the adapts using Service Fast Learn. Evaluate the
shifts and further learn pressures and volumes if
required.
• If a customer has a specific shift concern, the
Service Fast Learn should be skipped. Complete
the driving learn procedure to further learn
pressures and volumes for the complaint shift.
Transmission Adaptive Functions
The Hydra-Matic® 8-Speed RWD transmission utilizes
a line pressure and volume control system during
upshifts to compensate for new transmission build
variation as well as the normal wear of transmission
Copyright 2019 General Motors LLC. All Rights Reserved.
components. The variation from new and normal wear
of the apply components within the transmission over
time can cause shift time (the time required to apply a
clutch) to be longer or shorter than desired.
In order to compensate for these changes, the
transmission control module (TCM) adjusts the
pressure commands to the various pressure control
(PC) solenoids to maintain the originally calibrated shift
timing. The automatic adjusting process is referred to
as “adaptive learning” and it is used to ensure
consistent shift feel plus increase transmission
durability.
The TCM monitors the A/T input speed sensor (ISS)
and the A/T output speed sensor (OSS) during
commanded shifts to determine if a shift is occurring
too fast (harsh) or too slow (soft) and adjusts the
corresponding PC solenoid signal to maintain the set
shift feel. The purpose of the adapt function is to
automatically compensate the shift quality for the
various vehicle shift control systems. The adapt
function is a continuous process that will help to
maintain optimal shift quality throughout the life of the
vehicle.
How to Adapt Your Transmission
Transmission adapts can be reset and relearned on
most vehicles through GDS 2 by using the
Transmission Service Fast Learn procedure. This
procedure is completed in the service stall and no
vehicle driving is required.
Page 2
November, 2019
To complete the Transmission Service Fast Learn
procedure, enter GDS 2 Diagnosis and navigate to:
• Module diagnostics
• Transmission Control Module
• Configuration / Reset Function
• Transmission Service Fast Learn
Transmission Service Fast Learn is the recommended
method to reset and relearn adapts. This procedure is
available on all 2016-2018 MY Trucks, Cars and SUVs
with 8L45 and 8L90 Automatic Transmissions (RPOs:
M5U, M5T, M5N, M5X).
When the Service Fast Learn is complete, perform a
test drive and note any soft or harsh shifts.
To improve these complaint shifts further, locate the
clutches that need to be learned in the following table
below, and perform the required learning procedure for
each clutch listed in the chart. Execute the steps below
with the vehicle warmed up on a smooth level road. The
driver may observe a brief pulse behavior or firm shift
feel while the transmission is optimizing the clutch learn
characteristics.
Note: The transmission fluid temperature must be
between 35°C (95°F) and 95°C (203°F). Drive the
vehicle under normal conditions until this temperature
range is achieved. If the temperature is outside of this
range, the clutches will not be learned.
To Correct The
Shift Feel
Learn These Clutches
Applying
Clutch
Releasing
Clutch
1–2
C4
C3
2–3
C3
C1
3–4
C5
C3
4–5
C3
C4
5–6
C4
C2
6–7
C1
C4
7–8
C4
C3
3–1
C1
C4
C3
C4
2–1
Bulletin No.: 16-NA-019
Note: This sequence is MY 2016-2018 specific and
varies from MY 2015. The following adaptive
learning procedure was developed to further learn
clutch pressures and volumes required for specific
shifts. To expedite the learning process, it is
recommended to utilize a road with minimal traffic
volume that has as smooth and level surface as
possible.
Note: Within GDS2 a Transmission Service Fast Learn
Data page has been created to aid in performing
adaptive learn by showing throttle percentage, engine
speed, transmission fluid temperature, and gear
command.
To Learn C1 (For 6-7 or 3-1 Shift)
1. Pressure Learns:
Note: It is recommended to utilize a road with a speed
limit between of 48-72 km/h (30-45 mph) for this
procedure.
• Shift the transmission into 6th gear with the
PRNDM in the M position. Obtain an engine
speed between 1000 and 1600 engine rpm.
Maintain this condition for a total of about 8 km
(5 mi). Cruise control may be used and has
been found to result in faster learning of the
clutch values.
2. Volume Learns:
• Complete 15 light throttle 6-7 upshifts at
approximately 15% throttle to further learn C1.
To Learn C2 (For 6-5 Shift)
1. Pressure Learns:
Note: It is recommended to utilize a road with a speed
limit 64-72 km/h (40-45 mph) for this procedure.
• Perform 10 normal mode 6-5 coast down shifts
(zero/light brake) to learn the C2 Return Spring
pressure.
2. Volume Learns:
• Shift the transmission into 8th gear with the
PRNDM in the M position. Obtain an engine
speed between 1000 and 1750 rpm. Maintain
this condition for a total of about 8 km (5 mi).
Cruise control may be used and has been found
to result in faster learning of the clutch values.
N-D
C3 – Perform garage shift adaptive
learning
N-R
C5 – Perform garage shift adaptive
learning
To Learn C3 (For 2-3, 4-5, or N-D Shift)
Power Downshifts
Just perform the shifts and they will
adapt
Important: Application Specific Silverado & Sierra
e-Assist (RPO M5X) Trucks: To enable Adaptive
Learn on 8-7 Coast downs, a power on (~15% throttle
through the upshift) 7-8 upshift must be performed prior
to each downshift. This action enables torque converter
clutch (TCC) controlled slip on downshift to occur vs.
TCC unlocked, which occurs on normal downshifts and
disables Adaptive Learn. As a supplement, if the
Note: If the harsh shift is noted when the vehicle is
coming to a stop and shifting into 1st gear, this
downshift is most likely a 3-1 shift.
Bulletin No.: 16-NA-019
November, 2019
previous procedure is unsuccessful using GDS TCC
Control Functions, TCC can be left enabled during 8-7
Coast downs to aid in learning C3 pressure.
1. Pressure Learns:
• Perform 10 normal mode 8-7 coast down shifts
(zero/light brake) to learn the C3 Return Spring.
2. Volume Learns:
• Complete 15 light throttle 2-3 upshifts at
approximately 15% throttle to further learn C3.
To Learn C4 (For 1-2, 5-6, or 7-8 Shift)
1. Pressure Learns:
Note: It is recommended to utilize a road with a speed
limit between of 64-72 km/h (40-45 mph) for this
procedure.
• Shift the transmission into 7th gear with the
PRNDM in the M position. Obtain an engine
speed between 1000 and 1750 rpm. Maintain
this condition for a total of about 8 km (5 mi).
Cruise control may be used and has been found
to result in faster learning of the clutch values.
Important: Application Specific Express & Savana
Vans Pressure Learns: Perform 10 normal mode 7-6
coast down shifts (zero/light brake) to learn the C4
Return Spring.
2. Volume Learns:
• Complete 15 light throttle 1-2 upshifts at
approximately 15% throttle to further learn C4.
To Learn C5 (For 3-4 or N-R Shift)
1. Pressure Learns:
Note: It is recommended to utilize a road within a
Business Park or similar area, where it is safe to drive
at very slow speeds of approximately 8-40 km/h
(5-25 mph).
Page 3
Power Downshift Adaptive Learning
Starting with the vehicle operation in 8th gear, slowly
apply pressure to the accelerator pedal until downshift
occurs. Repeat as necessary in each gear (8, 7, 6, 5, 4,
3 and 2).
Note: This procedure will learn the off-going clutch
adapts for desired power downshift control.
Garage Shift Adaptive Learning (For N-D or N-R
Shift)
1. After above clutches are learned C3 –Drive and C5
– Reverse. With the vehicle at a stop, hold foot on
brake pedal and move the shifter from Neutral to
Drive and release the brake once in gear allowing
the vehicle to roll 5-10 feet or Neutral to Reverse
and release the brake once in gear allowing the
vehicle to roll 5-10 feet. Repeat as necessary until
desired shift quality is achieved.
Note: This procedure will learn the C13567 (C3-Drive)
and C45678R (C5 – Reverse) oncoming clutch adapts.
Warranty Information
For vehicles repaired under the Powertrain coverage,
use the following labor operation. Reference the
Applicable Warranties section of Investigate Vehicle
History (IVH) for coverage information.
Labor
Operation
Description
Labor Time
8480318*
Transmission Service Fast
Learn
Use Actual
Clock Time
*This is a unique Labor Operation for bulletin use only.
• Shift the transmission into 3rd gear with the
PRNDM in the M position. Start a very slow
acceleration, starting at about 1000 rpm.
Maintain the slow acceleration until you reach
about 2500 rpm. Once you reach 2500 rpm,
slow back down to 1000 rpm and repeat the
slow acceleration up to 2500 rpm. Repeat this
10 times.
2. Volume Learns:
• Complete 15 light throttle 3-4 upshifts at
approximately 15% throttle to further learn C5.
Version
3
Modified
August 19, 2016 – Added the 2017 Model Year and updated information.
November 13, 2019 – Added the 2018 Model Year and a Warranty statement.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these
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 your GM dealer for information on whether your vehicle may benefit from the
information.
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