File in Section:

Service Bulletin

Bulletin No.:
Date:

07 - Transmission/Transaxle
14-07-30-001B
December, 2014

INFORMATION
Subject:

Information on Transmission Adaptive Functions and Correcting Low Mileage Harsh
Shifts

Models:

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

This bulletin has been revised to add models and reference the Transmission Adaptive
Values Learn procedure. Please discard Corporate Bulletin Number 14-07-30-001A.

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
Transmission adapts can be reset and relearned on most vehicles through GDS 2 by using the Transmission
Adaptive Values Learn procedure. This procedure is completed in the service stall and no vehicle driving is required.
To complete the Transmission Adaptive Values Learn procedure enter GDS 2 Diagnosis and navigate to:
– Module diagnostics
– Transmission Control Module
– Configuration / Reset Function
– Transmission Adaptive Values Learn
Transmission Adaptive Values Learn is the recommended method to reset and relearn the adapts. This procedure is
available on all trucks. This procedure is also available on Corvettes built on September 29, 2014 or later. Use the
Investigate Vehicle History (IVH) to verify the build date of a Corvette.
Important: Transmission Adaptive Values Learn is shown as an available GDS 2 procedure on all 2015 Corvettes
built before September 29, 2014. This method is not effective and will not reset and relearn the adapts. These cars
must be driven to learn the adapts.
For Corvettes built before September 29, 2014 the Hydra-Matic® 8-Speed RWD transmission adaptive learn
process can only 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.

Perform a test drive and note any soft or harsh shifts.
To improve these complaint shifts, locate the clutches that need to be learned in the following table below, and
perform the required learning procedure for each clutch listed below the chart.
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
C4

2–1

C3

N-D

C3 – Perform garage shift adaptive learning

N-R

C5 – Perform garage shift adaptive learning

Power Downshifts

Just perform the shifts and they will adapt

Note: During low vehicle speeds with no accelerator pedal input downshift will most likely be a 3-1 shift.
To Learn C1:
Shift the transmission into 6th 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 5 miles (8 km). Cruise control may be used and has been found
to result in faster learning of the clutch values. Try the complaint shift to see if it has improved to an acceptable level.
If not, continue with operation in this speed range until the complaint shift improves.
To Learn C2:
Note: Perform abbreviated coast down shift adaptive learning procedure listed below to enable learn mode.
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 5 miles (8 km). Cruise control may be used and has been found
to result in faster learning of the clutch values. Try the complaint shift to see if it has improved to an acceptable level.
If not, continue with operation in this speed range until the complaint shift improves.
To Learn C3:
Note: Perform abbreviated coast down shift adaptive learning procedure listed below to enable learn mode.
Shift the transmission into 4th gear with the PRNDM in the M position. Start a slow acceleration at about 1000 rpm
and maintain the slow acceleration until you reach about 1650 rpm. Once you reach 1650 rpm, go back down to
1000 rpm and repeat the slow acceleration up to 1650 rpm. Repeat this a few times and re-try the complaint shift to
see if it has improved to an acceptable level. If it has not, continue this slow acceleration procedure until the
complaint shift improves.
To Learn C4:
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 5 miles (8 km). Cruise control may be used and has been found
to result in faster learning of the clutch values. Try the complaint shift to see if it has improved to an acceptable level.
If not, continue with operation in this speed range until the complaint shift improves.
To Learn C5:
Shift the transmission into 3rd gear with the PRNDM in the M position. Start a slow acceleration at about 1000 rpm
and maintain the slow acceleration until you reach about 2500 rpm. Once you reach 2500 rpm, go back down to
1000 rpm and repeat the slow acceleration up to 2500 rpm. Repeat this a few times and re-try the complaint shift to
see if it has improved to an acceptable level. If it has not, continue this slow acceleration procedure until the
complaint shift improves.

Abbreviated Coast Down Shift Adaptive Learning:
Lightly accelerate to 65 mph (105 km/h) and coast to 25 mph (40 km/h) (light braking can be applied). Repeat 10
times.
• This procedure will enable clutch apply adaptive learning for the C2 and C3.
Note: This only needs to be performed once per drive cycle to enable the adaptive learning for all subsequent C2
and C3 learning maneuvers. Failure to perform this procedure will result in no learning of these clutches.
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).
• This procedure will learn the off-going clutch adapts for desired power downshift control.
Garage Shift Adaptive Learning:
Perform abbreviated coast down shift adaptive learning procedure. Then with the vehicle at a stop, hold foot on
brake pedal and move the shifter from Neutral to Drive and Neutral to Reverse. Repeat as necessary until desired
shift quality is achieved.
• This procedure will learn the C13567 (C3-Drive) and C45678R (C5 – Reverse) oncoming clutch adapts.