GMC C-Series 2001 Owner's Manual page 236

Electric/Hydraulic Parking
Brake Fluid
If you have an electric/hydraulic parking brake, a good
time to check the fluid level is when you check the fluid
levels under the hood.
The fluid reservoir is located in the component box
under the driver's side of the cab.
If you need to add fluid, use Dexron
transmission fluid (GM Part Number 12345881).
6-34
How to Check and Add Fluid
First, apply the parking brake. To check the fluid level,
look at the MAX and MIN lines on the side of the
reservoir. If the level is below the MAX line, add fluid.
To add fluid, clean away any dirt around the reservoir
cap. Remove the reservoir cap and add enough fluid to
bring it up to the MAX level.
R
III automatic
NOTICE:
Always use proper fluid (automatic transmission
fluid), not brake fluid. Failure to use the proper
fluid can cause leaks and damage hoses and seals.