GMC Duramax Diesel 2015 Owner's Manual page 93

10-14 Vehicle Care
1. For areas where ambient
temperatures stay above 40°C
( 40°F), regular transmission
fluid can be used. See
Recommended Fluids and
Lubricants on page 11-8.
2. For areas where ambient
temperatures fall below 40°C
( 40°F), synthetic transmission
fluid approved to Allison
Transmission Specification
should be used. See
Recommended Fluids and
Lubricants on page 11-8. The
synthetic transmission fluid can
be used for all temperature
ranges.
How to Add Fluid
See Maintenance Schedule on
page 11-3 to determine what kind of
transmission fluid to use. See
Recommended Fluids and
Lubricants on page 11-8.
Using a funnel, add fluid down the
transmission dipstick tube only after
checking the transmission fluid
while it is hot. A cold check is used
only as a reference. If the fluid level
is low, add only enough of the
proper fluid to bring the level up to
the HOT area for a hot check.
It does not take much fluid,
generally less than 0.5 L (1 pt). Do
not overfill.
Caution
Use of the incorrect automatic
transmission fluid may damage
the vehicle, and the damage may
not be covered by the vehicle
warranty. Always use the
automatic transmission fluid listed
in Recommended Fluids and
Lubricants on page 11-8.
After adding fluid, recheck the
fluid level as described under
How to Check earlier in this
section.
When the correct fluid level is
obtained, push the dipstick back
in all the way. Then flip the
handle down to lock the dipstick
in place.