GMC 2005 Sierra Denali Owner's Manual page 294

How to Check
Because this operation can be a little difficult, you may
choose to have this done at the dealership service
department.
If you do it yourself, be sure to follow all the instructions
here, or you could get a false reading on the dipstick.
Notice: Too much or too little fluid can damage
your transmission. Too much can mean that some
of the fluid could come out and fall on hot engine
part or exhaust system parts, starting a fire.
Too little fluid could cause the transmission to
overheat. Be sure to get an accurate reading if you
check your transmission fluid.
Wait at least 30 minutes before checking the
transmission fluid level if you have been driving:
•
When outside temperatures are above 90°F (32°C).
•
At high speed for quite a while.
•
In heavy traffic — especially in hot weather.
•
While pulling a trailer.
To get the right reading, the fluid should be at normal
operating temperature, which is 180°F to 200°F
(82°C to 93°C).
5-22
Get the vehicle warmed up by driving about
15 miles (24 km) when outside temperatures are
above 50°F (10°C). If it is colder than 50°F (10°C), drive
the vehicle in THIRD (3) until the engine temperature
gage moves and then remains steady for 10 minutes.
A cold fluid check can be made after the vehicle
has been sitting for eight hours or more with the engine
off, but this is used only as a reference. Let the
engine run at idle for five minutes if outside
temperatures are 50°F (10°C) or more. If it is colder
than 50°F (10°C), you may have to idle the engine
longer. Should the fluid level be low during this cold
check, you must check the fluid hot before adding fluid.
Checking the fluid hot will give you a more accurate
reading of the fluid level.
Checking the Fluid Level
Prepare your vehicle as follows:
•
Park your vehicle on a level place. Keep the engine
running.
•
With the parking brake applied, place the shift lever
in PARK (P).
•
With your foot on the brake pedal, move the shift
lever through each gear range, pausing for about
three seconds in each range. Then, position the shift
lever in PARK (P).
•
Let the engine run at idle for three minutes or more.