GMC 2002 Yukon XL Owner's Manual page 347

Then, without shutting off the engine, follow these steps:
See "Engine Compartment Overview" in the Index for
more information on location.
6-26
The red transmission
dipstick handle with the
TRANS/LOCK text or
graphic is located at the rear
of the engine compartment,
on the passenger's side.
1. Flip the handle up and then pull out the dipstick and
wipe it with a clean rag or paper towel.
2. Push it back in all the way, wait three seconds and
then pull it back out again.
3. Check both sides of the dipstick, and read the lower
level. The fluid level must be in the COLD area,
below the cross–hatched area, for a cold check or in
the HOT area or cross–hatched area for a hot check.
4. If the fluid level is in the acceptable range, push the
dipstick back in all the way; then flip the handle
down to lock the dipstick in place.