GMC 1994 Sonoma Owner's Manual page 237

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.
Check the fluid level only when your engine is off, the vehicle is parked on
a level place and the transmission is cool enough for you to rest your fingers
on the trimmission case.
Then, follow these steps:
1. Remove the filler plug.
2. Check that the lubricant level is up to the bottom of the filler plug hole.
3. If the fluid level is good, install the plug and be sure it is fully seated. If
the fluid level is low, add more fluid as described in the next steps.
How to Add Fluid
Here's how to add fluid. Refer to the Maintenance Schedule to determine
what kind of fluid to use. See "Recommended Fluids and Lubricants" in the
Index.
1. Remove the filler plug.
2. Add fluid at the filler plug hole. Add only enough fluid to bring the
fluid level up to the bottom of the filler plug hole.
3. Install the filler plug. Be sure the plug is fully seated.
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