GMC 1994 Yukon Owner's Manual page 275

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 parts or exhaust system, starting a fire. 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).
To check trunsmissionfluid hot: Get the vehicle warmed up by driving
about 15 miles (24 km) when outside temperatures are above 50°F
(
10" C).
If it's colder than 50°F (1 0" C), drive the vehicle in "D" (3rd Gear) until the
engine temperature gage moves and then remains steady for ten minutes.
Then follow the hot check procedures.
To check transmissionfluid cold: A cold check is made after the vehicle has
been sitting for eight hours or more with the engine off and 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's colder than 50°F ( 1
OOC),
you may have to
idle the engine longer. Should the fluid level be low during a cold check,
you must perform a hot check before adding fluid. This will give you a more
accurate reading of the fluid level.
To check the fluid hot
or
cold
Park your vehicle
on
a level place.
With the parking brake applied, place the shift lever in "P" (Park).
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 "P" (Park).
Let the engine run at idle for three minutes or more.
Then, without shutting o f t h e engine, follow these steps:
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