File in Section:
Bulletin No.:

Service Bulletin

Date:

07 - Transmission/Transaxle
14-07-30-001
September, 2014

INFORMATION
Subject:

Information on Transmission Adaptive Functions

Models:

2015 Cadillac Escalade, Escalade ESV
2015 Chevrolet Corvette
2015 GMC Yukon
Equipped with 8L90 Automatic Transmission (RPO M5U)

Some customers may comment on low mileage
vehicles with automatic transmission that shift feel to be
too firm (harsh) or may slip or flare. 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.
Transmission Adaptive Functions
The Hydra-Matic® 8-Speed RWD transmission utilizes
a line pressure control system during upshifts to
compensate for new transmission build variation as
well as the normal wear of transmission components.
The variation experience on a 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
The Hydra-Matic® 8-Speed RWD transmission
adaptive learn process can be accomplished by driving
in the following manner. 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.
For a concern with a 1-2 upshift:
Manually select 7th gear using tap switches with the
shifter in the “M” position. Maintain a light acceleration
rate of the vehicle while keeping engine speed between
1000-1750 rpm. Repeat this light acceleration rate up to
10 times.
For a concern with a 3-1 coastdown (closed throttle)
shift:
Manually select 6th gear using tap switches with the
shifter in the “M” position. Maintain a light acceleration
rate of the vehicle while keeping engine speed between
1000-1750 rpm. Repeat this light acceleration rate up to
10 times.

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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