Service Bulletin

Bulletin No.:

22-NA-122

Date:

June, 2022

INFORMATION
Subject:

Diagnostic Tip for DTCs Set at a Low Mileage for 8L45/90 Automatic Transmissions
Model Year:

VIN:

Brand:

Model:

Cadillac

CT4

M5N

Chevrolet

to

from

to

Engine:

Transmission:

Camaro

M5T

Colorado

M5T

Express

M5U, MQD

Silverado 1500 - LTD
(RPO J21, VIN Digit
5 = W/Y)
Silverado 1500 - New
(RPO J22, VIN Digit
5 = A/D)

GMC

from

MQE
2022

2022

Canyon

M5T

Savana

M5U, MQD

Sierra 1500 - Limited
(RPO J21, VIN Digit
5 = 8/9)

MQE

Sierra 1500 - New
(RPO J22, VIN Digit
5 = H/U)

Involved Region or Country

North America, Middle East

Condition

Some customers may comment that the MIL is illuminated.

Cause

This condition may be caused by manufacturing debris that clears itself from the valve
body and then becomes captured by the filter.

Information

The purpose of this bulletin is to aid the service technician in diagnosing 8L45/90
automatic transmissions with low mileage and DTCs current or history related to the
transmission control solenoids and valves. Intent is to assist in diagnosing the correct
issue, minimize return customer visits for the same issue, and reduce unnecessary
repairs in cases of transient or momentary issues that may happen during vehicle initial
break-in period.
Follow the Service Procedure steps below to determine repair strategy.

Copyright 2022 General Motors LLC. All Rights Reserved.

Page 2

June, 2022

Important: Service agents must comply with all
International, Federal, State, Provincial, and/or
Local laws applicable to the activities it performs
under this bulletin, including but not limited to
handling, deploying, preparing, classifying,
packaging, marking, labeling, and shipping
dangerous goods. In the event of a conflict between
the procedures set forth in this bulletin and the
laws that apply to your dealership, you must follow
those applicable laws.
Important: Please refer to these service publications
for resolutions to customer comments prior to
proceeding with this bulletin:
• 21-NA-149: Engine Wire Harness Chafing
• 21-NA-275: Rear Wheel Lock Up, ABS Event,
Loud Bang and a Flashing “D” on Driver
Information Center (DIC) when Lightly or
Moderately Accelerating Forcing an 8-7 or 8-6
Downshift
• 20-NA-187: Delayed and/or Harsh Engagement of
Transmission Shift After Vehicle Sitting with
Engine Off
• 19-NA-136: Howling, Whining/Whirring, Shudder/
Vibration, and/or Grinding Noise While in 4HI, 4HI
Auto and/or During Parking Lot Maneuvers in
Auto Mode
• 16-NA-361: Information on Transmission Harsh
1-2 Shift Upon First Start Up/Shift of the Day
Under Light Throttle
• 16-NA-019: Information on Transmission Adaptive
Functions and Correcting Low Mileage Harsh
Shifts, Slips, or Flares
• 18-NA-285: Information on Slight Movement in
Park at Ignition On and Vehicle Start Up and/or
During a Remote Vehicle Start Event

Service Procedure
Step One — Check DTCs
Check all Modules for DTCs. Record all DTCs, Current
or History, and which Module the codes are in on the
work order.

Step Two — Road Test
Before the Road Test, Ensure the Following:
• The engine is performing properly. Often engine
misfires or engine lack of power for any reason
can cause erratic transmission shifting or
vibrations that may seem like torque converter
shudder concerns. Don’t overlook issues like
plugged or restricted exhaust.
• Don’t overlook engine or chassis DTCs that may
be related to the cause of the transmission shifting
concerns.
• Tire pressure is correct, and tires are matching
brand and of equal size. Different brand tires of
the same size can have different circumference
measurements.

Bulletin No.: 22-NA-122

Electrical Function Check:
Note: Perform this procedure first, in order to ensure
the electronic transmission components are functioning
properly. If these components are not checked, a
simple electrical condition could be misdiagnosed.
1. Connect the scan tool.
2. Ensure the gear selector is in PARK and set the
parking brake.
3. Start the engine.
4. Verify that the following scan tool data can be
obtained and is functioning properly:
• Engine Speed
• Transmission ISS
• Transmission OSS
• Vehicle Speed
• IMS
• Commanded Gear
• Gear Ratio
• Brake Pedal Position
• ECT (Included in GDS Engine Data List)
• Trans. Fluid Temp.
• Calc. Throttle Position
• Ignition Voltage
• Trans. Control Solenoid Valve 1-9
• TCC Slip Speed
5. Check the garage shifts.
– Apply the brake pedal and ensure the parking
brake is set.
– Move the gear selector through the following
ranges:
⇒ Park to Reverse
⇒ Reverse to Neutral
⇒ Neutral to Drive
⇒ Drive to Reverse
⇒ Reverse to Drive
– Pause 2 to 3 seconds in each gear position.
– Verify the gear engagements are immediate (less
than 3 seconds to complete if trans fluid
temperature is above 20°C) and not harsh. Note
that these shifts may be almost imperceptible in
some applications. Using the scan tool to monitor
Transmission ISS achieving 0 rpm can be used
to check delay in these cases.
Note: Harsh engagement may be caused by any of the
following conditions:
– High engine idle speed—Compare engine idle
speed to desired idle speed.
– Incorrect line pressure—Investigate
Transmission Control Solenoid Valve 6 Cmd.
– A default condition caused by certain DTCs that
result in maximum line pressure to prevent clutch
slippage.

Bulletin No.: 22-NA-122

June, 2022

– Incomplete adapting or incorrect adapting—
Repeat maneuver multiple times to see if shift
quality improves. If it does not, refer to service
procedures and field bulletins for Harsh Garage
Shift.
Note: Delayed engagement may be caused by any of
the following conditions:
– Low idle speed—Compare engine idle speed to
desired idle speed.
– Low fluid level.
– Incorrect line pressure—Investigate
Transmission Control Solenoid Valve 6 Cmd.
– Cold transmission fluid temperature (TFT)—Use
the scan tool to determine TFT.
– Selector linkage—Inspect and adjust as
necessary.
– Incomplete adapting or incorrect adapting—
Repeat maneuver multiple times to see if delay
improves. If it does not, refer to service
procedures and field bulletins for Harsh, Soft,
Delayed or Slipping First, Second, Seventh,
Eighth, or Reverse Shift.
6. Monitor transmission range on the scan tool,
transmission data list.
– Apply the brake pedal and ensure the parking
brake is set.
– Move the gear selector through all ranges.
– Pause 2 to 3 seconds in each range.
– Return gear selector to PARK.
– Verify that all selector positions match the scan
tool display.
7. Check throttle position input.
– Apply the brake pedal and ensure the parking
brake is set.
– Ensure the gear selector is in PARK.
– Monitor the scan tool Calc. Throttle Position
while increasing and decreasing engine speed
with the throttle pedal. The scan tool Calc.
Throttle Position percentage should increase and
decrease with engine speed.
If any of the above checks do not perform properly,
record the result for reference after completion of the
road test.
During the Road Test:
– Perform the test only when traffic conditions permit.
– Operate the vehicle in a controlled, safe manner.
– Observe all traffic regulations.
– Take along qualified help in order to operate the
vehicle safely and view the scan tool data while
conducting this test. Do not attempt to view data
while operating the vehicle yourself.
– Observe any unusual sounds or smells.
– Abort test if DTC/MIL resets at any point and follow
Service Information.

Page 3

Upshift Control and Torque Converter Clutch (TCC)
Apply:
The TCM calculates the upshift points based primarily
on 2 inputs: throttle position and vehicle speed. When
the TCM determines that conditions are met for a shift
to occur, the TCM commands the shift by varying
current to the appropriate transmission control
solenoids to control oncoming and offgoing clutch
pressures.
1. Monitor the following scan tool parameters:
• Calc. Throttle Position
• Vehicle Speed
• Engine Speed
• Transmission ISS
• Transmission OSS
• Commanded Gear
• Transmission Control Solenoid Valve 1-9
• TCC Slip Speed
2. Place the gear selector in the DRIVE position.
3. Accelerate the vehicle using a steady throttle
position between 15 and 20 percent. Hold the
throttle steady.
4. As the transmission upshifts, there should be a
noticeable shift feel or engine speed change within
1 to 2 seconds of the commanded gear change.
The transmission control solenoid valve pressure
command should change to “ON” for the oncoming
clutch and “OFF” for the offgoing clutch.
5. Note any harsh, soft or delayed shifts or slipping.
Note any noise or vibration.
6. The TCC feel may not be noticeable. In many
applications the TCC will apply after the 1-2 shift
and TCC events will not be easily detected using
engine speed.
Note: This transmission is equipped with an
electronically controlled capacity clutch (ECCC), which
allows operation of the clutch without fully locking to the
torque converter cover. The clutch maintains a small
amount of slippage, approximately 0-50 RPM,
depending on the vehicle application. TCC may apply
in 1st through 8th gear. ECCC was developed to
reduce the possibility of noise, vibration or chuggle
caused by TCC apply. Full lockup is available at
highway speeds on some applications.
7. Monitor Transmission Control Solenoid Valve 7
current while driving and check TCC slip speed
when the pressure command indicates that the
TCC is commanded to apply.
When the TCC applies, slip speed should be
controlled to below 100 RPM when the
transmission is not shifting, and the throttle is held
steady. If the TCC slip exceeds this value for more
than 6 seconds after the Transmission Control
Solenoid Valve 7 current indicates that the TCC is
commanded on:
– Check for DTCs.
– Refer to Torque Converter Diagnosis in SI.

Page 4

June, 2022

Part Throttle Step-In Downshifts:
1. Place the gear selector in the DRIVE position
2. Accelerate the vehicle at light throttle (5–15
percent) until 3rd gear is just achieved.
3. Quickly increase throttle angle until commanded
gear indicates that a downshift to 2nd gear is
commanded.
4. Verify that the transmission downshifts within 2
seconds of the throttle movement.
5. Repeat steps 2 to 4 at higher speed to achieve 4th
gear and then step in to command a 4th gear to 3rd
gear downshift.
6. Repeat steps 2 to 4 at higher speed to achieve 5th
gear and then step in to command a 5th to 4th gear
downshift.
7. Repeat steps 2 to 4 at higher speed to achieve 6th
gear and then step in to command a 6th gear to 5th
gear downshift.
8. Repeat steps 2 to 4 at higher speed to achieve 7th
gear and then step in to command to a 7th to 6th
gear downshift.
9. Repeat steps 2 to 4 at a higher speed to achieve
8th gear and then step in to command an 8th to 7th
gear downshift.
10. Note any harsh, soft or delayed shifts or slipping.
Note any noise or vibration.
Manual Downshifts:
Manual downshift testing is not required since all
vehicles equipped with the 8L90 are also equipped with
some form of Driver Control Mode (DCM). The TCM will
automatically override DCM downshifts to protect the
transmission from damage.
• Coasting Downshifts:
1. Place the gear selector in the DRIVE
position.
2. Accelerate the vehicle to 8th gear with the
TCC applied.
3. Release the throttle and apply the brakes.
4. Verify that the downshifts occur as
commanded by monitoring gear ratio, which
should change after commanded gear
changes.
Manual Gear Range Selection:
Perform the following test using a 10–15 percent
throttle position.
• Reverse:
1. With the vehicle stopped, move the gear
selector to REVERSE.
2. Slowly accelerate the vehicle.
3. Verify that there is no noticeable slip, noise or
vibration.

Bulletin No.: 22-NA-122

Note: Complete the test in the sequence given.
Incomplete testing cannot guarantee an accurate
evaluation.
Note: If the vehicle you are testing is a Hybrid/Electric
Vehicle and is equipped with an E-Assist or BAS
propulsion system, please refer to the applicable
vehicle Owner Manual/Supplement for a complete
description and an explanation of operating conditions
for the automatic stop/start feature. When performing
this Road Test, the auto stop/start must be verified to
ensure the shifting characteristics of this feature are
operating as designed
Driver Control Mode (DCM):
Refer to the owner's manual for specific instructions on
the type of DCM available in this application. Utilize the
DCM to ensure that the transmission responds
appropriately to driver's commands. The TCM will
upshift automatically when maximum engine speed is
achieved and will protect from any downshift which may
cause excessive engine RPMs.
Tow/Haul Mode:
Tow/Haul Mode Grade Braking is only enabled while
the Tow/Haul Mode is selected, and the vehicle is not in
the Range Selection Mode. See Manual Mode. Tow/
Haul Mode Grade Braking assists in maintaining
desired vehicle speeds when driving on downhill
grades by using the engine and transmission to slow
the vehicle.
See Towing Equipment.
After the Road Test, Check the Following:
⇒ Inspect for any diagnostic trouble codes (DTCs)
that may have set during the testing. Refer to the
applicable DTC information in Service Information
for diagnosis.
⇒ Monitor the scan tool data for any abnormal
readings or data.
⇒ Inspect for fluid leaks. Refer to Fluid Leak
Diagnosis in SI.
• If the codes could not be duplicated during the
road test, please return the vehicle to the
customer without attempting any repairs.
• If any DTCs reset, please follow Service
Information for the appropriate diagnostics.

Parts Information
No parts are required for this repair.

Bulletin No.: 22-NA-122

June, 2022

Page 5

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

8486178*

Diagnosing and Testing 8L45/90 Automatic Transmissions

0.8 hr

*This is a unique Labor Operation for Bulletin use only.

Version

1

Modified

Released June 17, 2022

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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