The transmission may get stuck intermittently in 1st gear on some 2024-2026 Traverse, Acadia; and 2025-2026 Enclave models equipped with the 8-speed 8T65 automatic transmission (RPO MF8). If this occurs, it will be necessary to stop the vehicle and shift to Park to correct the issue. (Fig. 3)
Fig. 3
The output speed sensor may briefly send an incorrect signal, which may cause the vehicle to follow an irregular shift pattern and get stuck in 1st gear until a shift-to-Park event is performed.
If this condition occurs, begin diagnosis by verifying there are not any DTCs set. If any DTCs are set, follow the diagnostic procedures in the appropriate Service Information for each DTC before performing any other repairs.
Once it has been verified that no DTCs set and that the transmission gets stuck in 1st gear, replace the output speed sensor in the transmission. (Fig. 4, #2) Refer to Automatic Transmission Output Speed Sensor Replacement in the Service Information.
Fig. 4
Replace Output Speed Sensor
The output speed sensor is located behind the control valve solenoid body. Remove the control valve body cover, wiring harness, Park inhibitor solenoid, control valve solenoid body, and fluid transfer pipe to access the output speed sensor.
After installing the new output speed sensor, use DT-36850-A Transjel Lubricant to install the four control valve body ball check valves. Do not place check balls in the pockets indicated by arrows in the installation procedure. (Fig. 5) If check balls are placed in these locations, there will be shift quality concerns.
Fig. 5
Refer to Bulletin #26-NA-192 for additional details, including part numbers.
– Thanks to Matt Razz
