GMC Sierra Owners Manual
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 desired range of gears.
To use this feature, do the following:
1. Move the shift lever to M(Manual Mode).
2. Press the plus/minus buttons, located on the steering column shift lever, to select the desired range of gears for current driving conditions.
When M(Manual Mode) is selected a number displays next to the M, indicating the current gear.
This number is the highest gear that can be used. However, the vehicle can automatically shift to lower gears as it adjusts to driving conditions. This means that all gears below that number are available. When 5 (Fifth) is selected, 1 (First) through 5 (Fifth) gears are automatically shifted by the vehicle, but 6 (Sixth) cannot be used until the plus/minus button located on the steering column lever is used to change to the gear.
Grade Braking is not available when Range Selection Mode is active.
See Tow/Haul Mode on page 9‑42.
While using Range Selection Mode, Cruise Control and the Tow/Haul Mode can be used.
If the vehicle has an exhaust brake, it can also be used, but will not automatically downshift the transmission. See Exhaust Brake in the Duramax Diesel supplement.
Notice: Spinning the tires or holding the vehicle in one place on a hill using only the accelerator pedal may damage the transmission. The repair will not be covered by the vehicle warranty. If you are stuck, do not spin the tires. When stopping on a hill, use the brakes to hold the vehicle in place.
Low Traction Mode
If your vehicle has the Allison Transmission, or the Hydra-Matic 6-Speed Automatic Transmission, it has a Low Traction Mode that can assist in vehicle acceleration when road conditions are slippery, such as with ice or snow. While the vehicle is at a stop, select the second gear range using Range Selection Mode. This will limit torque to the wheels after it detects wheel slip, preventing the tires from spinning.