20NA187

Bulletin No.:
Service Bulletin
Date:
20-NA-187
September, 2020
TECHNICAL
Subject:
Brand:
Cadillac
Chevrolet
GMC
Delayed and/or Harsh Engagement of Transmission Shift After Vehicle Sitting with
Engine Off
Model:
Model Year:
VIN:
from
to
Engine:
Transmission
(Automatic):
from
to
ATS
2018
2019
CTS
2018
2019
CT4
2021
2021
M5N
CT6
2018
2019
M5N, M5X
M5T, M5N, M5U
Camaro
2018
2021
M5T, M5N, M5U
Colorado
2018
2021
M5T
Corvette
2018
2019
M5U
M5U, MQD
Express
2018
2020
Silverado
2018
2018
Silverado LD
2019
2019
Silverado 1500
(New Model)
2019
2021
—
—
—
M5U, M5X, MQE
Canyon
2018
2021
M5T
Savana
2018
2021
M5U, MQD
Sierra
2018
2018
Sierra Limited
2019
2019
Sierra 1500
(New Model)
2019
2021
Involved Region or Country
Condition
M5U, M5X, MQE
North America, Europe
Some customers may comment on a condition of delayed engagement when the
transmission is shifted from Park to Reverse or Park to Drive after the vehicle has been
sitting with the engine off.
Note: This condition may typically occur after several hours or more commonly
overnight.
Customers may describe this condition as:
• Vehicle delaying into gear
• Feeling like the transmission is slipping
• Delayed engagement followed by a harsh engagement
Information
Copyright 2020 General Motors LLC. All Rights Reserved.
General Motors allows 3 seconds for the transmission to complete a garage shift, shifting
from Park to Reverse or Park to Drive. If the engine speed is increased before the
transmission has engaged, the garage shift may be harsh.
Operation will be normal for the subsequent engagements throughout the day and the
condition will not occur until the vehicle sits again with the engine off for several hours or
overnight.
Page 2
September, 2020
Bulletin No.: 20-NA-187
Service Procedure
Delayed Engagement Test:
Note: Vehicle should only be evaluated after sitting for
a minimum of 8 hours but less than 24 hours. To be
measured at 10°C (50°F) and above.
Delayed Engagement Park to Reverse or Drive is
present if the time difference between Gear Selected
(Pt. 1) and Transmission Input Shaft Speed reaching 0
RPMs (Pt. 2) exceeds 3 seconds. Foot is HELD on
Brake during maneuver.
4606651
If the customer describes the condition as a delayed or
slow engagement time with or without a harsh or bump
engagement feel when shifting the vehicle from Park to
Drive or Reverse, use GDS and monitor engine RPM
and the transmission Input Speed Sensor (ISS) prior to
starting the engine. Start the engine with the
transmission in Park. Shift the vehicle from Park to
Drive or Reverse leaving the service brake applied. The
ISS should drop to zero “0’ within 3 seconds; this is
clutch engagement time. Recording a GDS session log
can be useful in diagnosing this condition.
In most cases the transmission will engage in 3
seconds or less, which is considered an acceptable
engagement time and no repairs should be attempted.
If the vehicle has less than 4000 km (2500 mi), the
transmission or valve body has been replaced or a
clutch repair, follow the clutch learn procedure in
Service Bulletin #16-NA-019 to learn the C5 Reverse
and C3 Drive Clutch.
If engagement time exceeds 3 seconds, refer to the
following procedures:
– Attempt to learn the C3 – Drive and C5 Reverse Clutch using the following steps:
1. Allow the transmission sump temperature to rise
between 20° and 30°C (68° and 86°F).
Bulletin No.: 20-NA-187
September, 2020
Page 3
Note: DO NOT apply the accelerator pedal.
2. Perform 20 Park to Reverse shifts or 20 Park to
Drive shifts releasing the brake pedal with each
shift, allowing the vehicle to roll 5-10 feet (1.5-3.0
m) per engagement into gear.
– If the learn procedure does not correct the condition,
disassemble the transmission and inspect the
1-3-5-6-7 Clutch (C3) for a delay into Drive and
inspect the 4-5-6-7-8 Reverse Clutch (C5) for a delay
into Reverse. The respective clutch plates and seals
should be inspected for wear and or damage and
repaired accordingly.
Parts Information
No parts are required for this repair.
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
8481068*
Evaluate Transmission
Engagement Time
0.3 hr
Add
Perform C3 and C5 Clutch
Learn
0.2 hr
*This is a unique Labor Operation for bulletin use only.
Version
1
Modified
Released September 09, 2020
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.
WE SUPPORT VOLUNTARY
TECHNICIAN
CERTIFICATION