9th-Gear Operation on 9-Speed Transmissions

Transmission operation on some 2018-2022 Terrain; 2019-2022 XT4; 2020-2022 Encore GX, XT5, XT6, Acadia; and 2021-2022 Envision and Trailblazer models may not be fully understood by owners, especially at highway speeds. (Fig. 31) These models feature the 9T45, 9T50, or 9T60 9-speed transmission (RPO M3F, M3G, M3H, M3T, M3U). In some cases, drivers may feel that the transmission doesn’t shift into 9th gear or maintain 9th gear operation as expected.


Fig. 31


The 9-speed transmissions use all nine gears when it is most efficient to do so. The vehicle’s control system senses the operating conditions and determines the correct gear to deliver optimum performance and fuel economy.

The control calibration is tailored for each vehicle application and engine type. For example, optimal fuel economy during highway driving may actually be achieved in 8th gear rather than 9th gear depending on a number of factors, including vehicle speed, engine load and throttle input. 9th gear is engaged when appropriate.

Replacing transmission components or complete assemblies will not change the shifting operation of the transmission. (Fig. 32) To ensure 9th gear is operating properly, verify 9th gear is not being commanded on a test drive. Next, use GDS2 to manually command 9th gear. If achieved, the vehicle system is operating correctly.


Fig. 32


For additional information, refer to Bulletin #21-NA-181.


– Thanks to Mark Kevnick

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