GMC Sierra Owners Manual

Automatic Transmission
Driving and Operating / Automatic Transmission

If the vehicle is a hybrid, see the hybrid supplement for more information.

Vehicles with an automatic transmission have an electronic shift position indicator within the instrument panel cluster. This display comes on when the ignition key is turned to the ON/RUN position.

There are several different positions for the shift lever.

GMS Sierra: Automatic Transmission. Hydra-Matic 4-Speed Automatic Transmission
Hydra-Matic 4-Speed Automatic Transmission

GMS Sierra: Automatic Transmission. Heavy Duty 6-Speed Automatic Transmission Shown (Light Duty 6-Speed Similar)
Heavy Duty 6-Speed Automatic Transmission Shown (Light Duty 6-Speed Similar)

See Range Selection Mode under Manual Mode on page 9‑41.

P (Park): This position locks the rear wheels. It is the best position to use when starting the engine because the vehicle cannot move easily. When parked on a hill, especially when the vehicle has a heavy load, you might notice an increase in the effort to shift out of P (Park). See Torque Lock under Shifting Into Park on page 9‑33 for more information.

WARNING
It is dangerous to get out of the vehicle if the shift lever is not fully in P (Park) with the parking brake firmly set. The vehicle can roll.

Do not leave the vehicle when the engine is running unless you have to. If you have left the engine running, the vehicle can move suddenly. You or others could be injured. To be sure the vehicle will not move, even when you are on fairly level ground, always set the parking brake and move the shift lever to P (Park).

See Shifting Into Park on page 9‑33. If you are pulling a trailer, see Driving Characteristics and Towing Tips on page 9‑80.

WARNING
If you have Four-Wheel Drive, the vehicle will be free to rolleven if the shift lever is in P (Park)if the transfer case is in Neutral. So, be sure the transfer case is in a drive gear, Two-Wheel Drive High or Four-Wheel Drive High or Four-Wheel Drive Lownot in Neutral. See Shifting Into Park on page 9‑33.

R (Reverse): Use this gear to back up.

Notice: Shifting to R (Reverse) while the vehicle is moving forward could damage the transmission. The repairs would not be covered by the vehicle warranty. Shift to R (Reverse) only after the vehicle is stopped.

To rock the vehicle back and forth to get out of snow, ice, or sand without damaging the transmission, see If the Vehicle Is Stuck on page 9‑16.

N (Neutral): In this position, the engine does not connect with the wheels. To restart when you are already moving, use N (Neutral) only. Also, use N (Neutral) when the vehicle is being towed.

WARNING
Shifting into a drive gear while the engine is running at high speed is dangerous. Unless your foot is firmly on the brake pedal, the vehicle could move very rapidly.

You could lose control and hit people or objects. Do not shift into a drive gear while the engine is running at high speed.

Notice: Shifting out of P (Park) or N (Neutral) with the engine running at high speed may damage the transmission. The repairs would not be covered by the vehicle warranty. Be sure the engine is not running at high speed when shifting the vehicle.

D (Drive): This position is for normal driving. It provides the best fuel economy. If you need more power for passing, and you are:

Going less than about 55 km/h (35 mph), push the accelerator pedal about halfway down.

Going about 55 km/h (35 mph) or more, push the accelerator all the way down.

By doing this, the vehicle shifts down to the next gear and has more power.

D (Drive) can be used when towing a trailer, carrying a heavy load, driving on steep hills, or for off-road driving. You might want to shift the transmission to a lower gear selection if the transmission shifts too often.

Downshifting the transmission in slippery road conditions could result in skidding. See Skidding under Loss of Control on page 9‑5.

The vehicle has a shift stabilization feature that adjusts the transmission shifting to the current driving conditions in order to reduce rapid upshifts and downshifts. This shift stabilization feature is designed to determine, before making an upshift, if the engine is able to maintain vehicle speed by analyzing things such as vehicle speed, throttle position, and vehicle load.

If the shift stabilization feature determines that a current vehicle speed cannot be maintained, the transmission does not upshift and instead holds the current gear.

In some cases, this could appear to be a delayed shift, however the transmission is operating normally.

The transmission uses adaptive shift controls. Adaptive shift controls continually compares key shift parameters to pre-programmed ideal shifts stored in the transmissions computer. The transmission constantly makes adjustments to improve vehicle performance according to how the vehicle is being used, such as with a heavy load or when temperature changes. During this adaptive shift control process, shifting might feel different as the transmission determines the best settings.

When temperatures are very cold, the Allison Transmission and Hydra-Matic 6-Speed transmission's gear shifting could be delayed providing more stable shifts until the engine warms up. Shifts could be more noticeable with a cold transmission. This difference in shifting is normal.

M(Manual Mode): This position is available on vehicles with the Allison Transmission or Hydra-Matic 6-Speed transmission. It lets drivers select the range of gears appropriate for current driving conditions. If the vehicle has this feature, see Range Selection Mode under Manual Mode on page 9‑41.

3 (Third): This position is also used for normal driving. It reduces vehicle speed more than D (Drive) without using the brakes. You might choose 3 (Third) instead of D (Drive) when driving on hilly, winding roads, when towing a trailer, so there is less shifting between gears and when going down a steep hill.

2 (Second): This position reduces vehicle speed even more than 3 (Third) without using the brakes.

You can use 2 (Second) on hills.

It can help control vehicle speed as you go down steep mountain roads, but then you would also want to use the brakes off and on.

If you manually select 2 (Second) in an automatic transmission, the transmission will start in second gear. You can use this feature for reducing the speed of the rear wheels when you are trying to start the vehicle from a stop on slippery road surfaces.

1 (First): For the Hydra-Matic 4-Speed transmission this position reduces vehicle speed even more than 2 (Second) without using the brakes. You can use it on very steep hills, or in deep snow or mud. If the shift lever is put in 1 (First) while the vehicle is moving forward, the transmission does not shift into first gear until the vehicle is going slowly enough.

For an Allison Transmission or Hydra-Matic 6-Speed transmission, this position reduces vehicle speed without using the brakes. You can use it for major/severe downgrades and off-road driving where the vehicle would otherwise accelerate due to steepness of grade. When you shift to 1 (First) it provides the lowest gear appropriate to current road speed and continues to downshift as the vehicle slows, eventually downshifting to 1 (First) gear.

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.


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