The 10-speed automatic transmission (RPO MGM, MGU, MHO, MHS, MHT, MHU, MHX, MKM, MQA, MQB, MQC, MQ2, MI2) on some 2023 CT4, CT5, Silverado, Sierra, Escalade; and 2023-2024 Silverado 2500 HD/3500 HD and Sierra 2500 HD/3500 HD models may not shift and defaults to 5th gear. DTC P0747 (Transmission Control Solenoid Valve 1 Stuck On) may be set in the Transmission Control Module (TCM). DTC P0747 will set with a hydraulic/mechanical condition in the transmission.
The shift condition may be due to the Transmission Control Valve Body failing, which likely caused DTC P0747 to set and for the transmission to default to 5th gear. In most cases, only the control valve body requires replacement. (Fig. 21)
Fig. 21
Before making any repairs, check the condition of the transmission fluid. As the vehicle accumulates mileage, the transmission fluid will darken from thermal cycles and use. The fluid should not have a burnt odor and there should not be clutch debris in the pan.
If the fluid shows good color with no evidence of clutch material, only replace the control valve body. (Fig. 22)
Fig. 22
A transmission with fluid that may be darker in color with minimal evidence of clutch material, and without any burnt odor, also should be serviced only with a control valve body. (Fig. 23)
Fig. 23
Fluid that shows extreme distress along with clutch material in the pan will require that the transmission be removed from the vehicle for further inspection to determine the clutches that have been damaged. (Fig. 24) Any suspect clutch should be repaired following the appropriate Service Information. The control valve body should be replaced as well.
Fig. 24
For more details, refer to Bulletin #24-NA-088.
– Thanks to Mark Gordon
yep and parts unavailable for months .