Information on Malfunction Indicator Lamp (MIL) Illuminated – Multiple DTCs Set – 2020-2021 Buick & Chevrolet

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Copyright 2020 General Motors LLC. All Rights Reserved.
Service Bulletin Bulletin No.: 20-NA-120
Date: June, 2020
INFORMATION
Subject: Information on Malfunction Indicator Lamp (MIL) Illuminated – Multiple DTCs Set
Brand: Model:
Model Year: VIN:
Engine: Transmission:
from to from to
Buick Encore GX 2020 2020
— — —
Automatic
Chevrolet (RPO MRG)
Malibu 2019 2020
Trailblazer 2021 2021
Involved Region or Country North America
Condition
Some customers may comment that the MIL is illuminated. If the vehicle has set one of
the DTCs listed below and the vehicle has been driven more than 48 km (30 mi) (check
DTC data for miles since DTC set), the transmission drive chain or pulleys could be
damaged. Use the inspection procedure below to check for possible damage. Also, if
during diagnosis of the vehicle the fluid level is observed to be low, 1.0 L (34.0 oz) or
more, the chain and pulleys should be inspected for possible damage.
• P0601
• P0604
• P0658
• P0746
• P0776
• P0796
• P0960
• P0961
• P0962
• P0963
• P0964
• P0965
• P0966
• P0967
• P0970
• P2670
Cause
When these DTCs set, the transmission will default to maximum pressure to protect from
damage, however, driving under this maximum condition for too long can damage the
drive system. Also, if the vehicle is operated with a low fluid level, it may cause the chain
to slip and cause drive system damage.
Correction
Note: Borescope SRV3880LNR or equivalent should be used for inspection. The
borescope needs to be one that can be articulated. In the U.S, GM has the borescope
available in the U.S. dealer loaner program.
Inspect the pulley surfaces and chain pin ends for chain slip marks and pulley grooving or
scuffing marks with a borescope. The damage typically is most visible on the chain ends
but the pulley surface should be checked as well.
Page 2 June, 2020 Bulletin No.: 20-NA-120
Service Procedure
5171810
The pulley and chain can be accessed through the
transmission fluid filler cap (1) at the top of the
transmission.
1. Insert the borescope between the chain guard
pivot and the inside edge of the primary pulley.
5608025
– Borescope image should look like the example
above.
Bulletin No.: 20-NA-120 June, 2020 Page 3
2. Inspect the chain pin ends.
5608011
• If the pin ends have no signs of slip marks, the
transmission is OK to be repaired for the cause
of the DTC/low fluid level.
5608015
• If the pin ends have signs of slip marks, the
transmission should be replaced, not repaired.
Page 4 June, 2020 Bulletin No.: 20-NA-120
3. Inspect for a damaged pulley surface.
5608026
• If the pulley surfaces do not show signs of
damage, the transmission is OK to be repaired
for the cause of the DTC/low fluid level.
5608042
• If the pulley surfaces show signs of surface
grooving and scuffing, the transmission should
be replaced, not repaired.
Parts Information
No parts are required for this repair.
Version 1
Modified Released June 01, 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.
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