Torque Lock
Torque lock is when the weight of the vehicle puts too much force on the parking pawl in the transmission. This happens when parking on a hill and shifting the transmission into P (Park) is not done properly and then it is difficult to shift out of P (Park). To prevent torque lock, set the parking brake and then shift into P (Park). To find out how, see “Shifting Into Park” listed previously.
If torque lock does occur, the vehicle may need to be pushed uphill by another vehicle to relieve the parking pawl pressure, so you can shift out of P (Park).
See also:
Range Selection Mode (Allison® Transmission or Hydra-Matic® 6-Speed
Transmission)
The vehicle may have a Range Selection Mode. The Range Selection Mode helps control the vehicle's transmission and vehicle speed while driving down hill or towing a trailer by letting you select a d ...
Electronic Range Select (ERS) Mode
ERS or manual mode allows for the selection of the range of gear positions. Use
this mode when driving down hill or towing a trailer to limit the top gear and vehicle
speed.
To use this feature:
...
Warranty
OnStar equipment may be warranted as part of the new-vehicle limited warranty.
The manufacturer of the vehicle furnishes detailed warranty information. ...