6.

⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒
⇒

– Low idle speed – Compare engine idle
speed to desired idle speed.
– Low fluid level.
– 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, record on the
repair order and replace the transmission
assembly.
Check Upshifts – 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 PC solenoids to control oncoming and
off going clutch pressures.
6.1. Monitor the following scan tool parameters:
Calc. Throttle Position
Vehicle Speed
Engine Speed
Transmission ISS
Transmission OSS
Command Gear
TCC PC Sol. Pressure Cmd.
TCC Slip Speed
TFP Switch 1
TFP Switch 2
TFP Switch 3
TFP Switch 4
PC Sol. 2 Pressure Cmd.
PC Sol. 3 Pressure Cmd.
PC Sol. 4 Pressure Cmd.
PC Sol. 5 Pressure Cmd.
Shift Solenoid 1 and 2
6.2. Place the gear selector in the DRIVE position.
6.3. Accelerate the vehicle using a steady throttle
position between 15 and 20 percent. Hold the
throttle steady.

Bulletin No.: 20-NA-136

6.4. 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 PC solenoid pressure command
should change to “YES” for the oncoming
clutch and the PC solenoid pressure
command should change to “NO” for the off
going clutch.
6.5. Note any harsh, soft or delayed shifts or
slipping. Note any noise or vibration.
6.6. The torque converter clutch (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. Monitor TCC PC solenoid
pressure command while driving and check
TCC slip speed when the pressure command
indicates that the TCC is commanded to
apply.
6.7. 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 TCC
PC Sol. Pressure Command indicates that the
TCC is commanded on:
⇒ Check for DTCs.
⇒ Refer to Torque Converter Diagnosis in SI.
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 20 RPM, in 2nd, 3rd,
4th, 5th, and 6th gears, depending on the vehicle
application. 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. Part Throttle Step-in Downshifts:
7.1. Place the gear selector in the DRIVE position.
7.2. Accelerate the vehicle at light throttle (5-10
percent) until 3rd gear is just achieved.
7.3. Quickly increase throttle angle until
commanded gear indicates that a downshift to
2nd gear is commanded.
7.4. Verify that the transmission downshifts within
2 seconds of the throttle movement.
7.5. 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.
7.6. Repeat steps 2 to 4 at higher speed to
achieve 5th gear and then step in to
command a 5th to 4th gear downshift.
7.7. 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.
7.8. Note any harsh, soft or delayed shifts or
slipping. Note any noise or vibration.

Bulletin No.: 20-NA-136

June, 2021

8. Coasting Downshifts:
8.1. Place the gear selector in the DRIVE position.
8.2. Accelerate the vehicle to 6th gear with the
TCC applied.
8.3. Release the throttle and apply the brakes.
8.4. Verify that the downshifts occur as
commanded by monitoring gear ratio, which
should change after commanded gear
changes.
8.5. Note any harsh, soft or delayed shifts or
slipping. Note any noise or vibration.
9. Reverse:
9.1. With the vehicle stopped, move the gear
selector to REVERSE.
9.2. Slowly accelerate the vehicle to a 10-15
percent throttle position.
9.3. Verify that there is no noticeable slip, noise or
vibration.
10. Road Test Results:
10.1. Diagnostic TIP : If completion of the above
tests are inconclusive to isolate if the
transmission shifting concern(s) are internal
transmission or input/command, can use the
control function feature in GDS2 to
command all shifts. If when using GDS2 to
command shifts and transmission shifts into
each range commanded, the concern is
generally an input/command concern, and
not an internal transmission concern. If
ranges are not completed when using GDS2
to command, then generally the concern is
an internal transmission concern and not an
input/command concern.
10.2. If one of these conditions is present during
the road test, document on the repair order
and replace the transmission assembly:
⇒ Vehicle does not move in drive
⇒ Vehicle does not move in reverse
⇒ There is a harsh garage shift
⇒ There is no park gear
10.3. If noise or vibration concern is noted, follow
Noise and Vibration Analysis in SI using
Chassis Ears and PICO scope in diagnosis.
10.4. If upshifts and downshifts are harsh, soft,
delayed, or slip, follow SI diagnosis for
condition.

Step Five — DTC
If any of the following DTCs are Current or reset during
the road test, record on the repair order and follow the
instructions below for that DTC.
Replace the transmission assembly if any one of these
DTCs is current or reset on road test.
• P0796 Transmission Control Solenoid Valve 3
Stuck Off
• P0797 Transmission Control Solenoid Valve 3
Stuck On
• P2723 Transmission Control Solenoid Valve 5
Stuck Off

•

Page 5

P2724 Transmission Control Solenoid Valve 5
Stuck On
• P18A8 Transmission Park Control Solenoid
Actuator Stuck Off
• P27EC Transmission Range Control Valve 1
Position Switch Performance
• P27F0 Transmission Range Control Valve 2
Position Switch Performance
If any one of these DTCs is current or reset on the road
test and the transmission fluid is red, translucent, and
doesn’t not have a burnt smell, then replace the
solenoid body and valve body.
• P0746 Transmission Control Solenoid Valve 1
Stuck Off
• P0747 Transmission Control Solenoid Valve 1
Stuck On
• P2731 Transmission Control Solenoid Valve 6
Performance
• P2732 Transmission Control Solenoid Valve 6
Stuck Off
• P2733 Transmission Control Solenoid Valve 6
Stuck On
• P2820 Transmission Control Solenoid Valve 9
Stuck Off
• P2821 Transmission Control Solenoid Valve 9
Stuck On
• P187D Transmission Park Valve Stuck On
• P187E Transmission Park Valve Stuck Off
• P18E7 Transmission Park Valve Position Sensor
1 Performance
• P18E8 Transmission Park Valve Position Sensor
2 Performance
• P18AA Transmission Range Control Valve 1
Position Switch Circuit Stuck On
• P18AB Transmission Range Control Valve 1
Position Switch Circuit Stuck Off
• P18AC Transmission Range Control Valve 2
Position Switch Circuit Stuck On
• P18AD Transmission Range Control Valve 2
Position Switch Circuit Stuck Off
• P18AE Transmission Range Control Enable Valve
Stuck Off
If any one of these DTCs is current or reset on the road
test and the transmission fluid is red, translucent, and
doesn’t not have a burnt smell, then replace the
solenoid body.
• P0741 Torque Converter Clutch (TCC) System
Stuck Off
• P0776 Transmission Control Solenoid Valve 2
Stuck Off
• P0777 Transmission Control Solenoid Valve 2
Stuck On
• P2817 Transmission Control Solenoid Valve 8
Stuck Off
• P2818 Transmission Control Solenoid Valve 8
Stuck On

Page 6

June, 2021

If any one of these DTCs is current or reset on the road
test and the transmission fluid is red, translucent, and
doesn’t not have a burnt smell, then replace the
valve body.
• P2714 Transmission Control Solenoid Valve 4
Stuck Off
• P2715 Transmission Control Solenoid Valve 4
Stuck On
If any one of these DTCs is current or reset on the road
test and the transmission fluid is red, translucent, and
doesn’t not have a burnt smell, then follow SI diagnostic
for output speed sensor.
• P0721 Output Speed Sensor Performance
• P0722 Output Speed Sensor Circuit No Signal
• P0723 Output Speed Sensor Circuit Intermittent
If any of these DTCs is History and are not able to be
reproduced, perform the Transmission Service Fast
Learn Procedure. If no DTCs, reset and return the
vehicle to the customer.
Symptoms other than listed above should be diagnosed
using SI procedures and repaired as necessary. If parts
needed to complete transmission repair are internal to
the transmission, then transmission assembly
replacement should be performed.
Note: The intent of this pilot is to favor replacement
over internal repair. If diagnosis determines internal
repairs are the root cause, further disassembly should
not occur, and the unit should be replaced.

Bulletin No.: 20-NA-136

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

Perform Fluid Level and Oil
Pressure Checks and
Service Fast Learn

1.5 hrs

8481048*
8464670**

Transmission Replacement

8463690***

Control Valve Body
Replacement

8463700

Control Valve Solenoid Body
Replacement

Use
Published
Labor
Operation
Time

8462260

Transmission Output Speed
Sensor Replacement

*This is a unique Labor Operation for bulletin use only. This
operation is only used if transmission assembly is not
replaced.
**Because the transmission is not to be disassembled for
this bulletin, the 1.5 hours add time for “Disassemble,
Inspect, Determine Repair and Re-assemble for Core
Return” should not be claimed.
***If valve body and solenoid body are replaced at the same
time use this labor operation.

Version

4

Modified

Released June 26, 2020
Revised August 18, 2020 – Added the Warranty Information section.
Revised September 25, 2020 – Added the 2021 Model Year.
Revised May 26, 2021 - Update information in the Overview section, Step One-DTC
section, Step Five DTC section and the Warranty Information section.

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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