GMC 2009 Yukon XL Owner's Manual page 532

Parking Brake and Automatic
Transmission P (Park) Mechanism
Check
CAUTION:
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When you are doing this check, the vehicle could
begin to move. You or others could be injured and
property could be damaged. Make sure there is
room in front of the vehicle in case it begins to roll.
Be ready to apply the regular brake at once should
the vehicle begin to move.
6-12
Park on a fairly steep hill, with the vehicle facing downhill.
Keeping your foot on the regular brake, set the parking
brake.
•
To check the parking brake's holding ability: With the
engine running and transmission in N (Neutral),
slowly remove foot pressure from the regular brake
pedal. Do this until the vehicle is held by the parking
brake only.
•
To check the P (Park) mechanism's holding ability:
With the engine running, shift to P (Park). Then
release the parking brake followed by the regular
brake.
Contact your dealer/retailer if service is required.
Hood and Liftgate Support Gas Strut
Service
Visually inspect gas strut for signs of wear, corrosion,
cracks, loss of lubricant, or other damage. Check
the hold open ability of gas strut. If necessary, replace
with genuine parts from your dealer/retailer.