1998 GMC Sonoma Owner's Manual - Page 270

How to Add Fluid Refer to the Maintenance Schedule to determine what kind of transmission fluid to use. See "Recommended Fluids and Lubricants" in the Index. Add fluid 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 bringthe level up to the HOT area for a hot check. It doesn't take much fluid, generally less than one pint (0.5 L). Don 7 overfill. Manual Transmission Fluid When to Check A good time to have it checked is when the engine oil is changed. However, the fluid in your manual transmission doesn't require changing. How to Check Because this operation can be a little difficult, you may choose to have this done at your GM dealership Service Department. NOTICE: We recommend you use only fluidlabeled DEXRON@-111, because fluidwith that label is made especially for your automatic transmission. Damage causedby fluid other than DEXRON-111 is not coveredby your new vehicle warranty. After adding fluid, recheck the fluid level as described under "How to Check." 0 If you do it yourself, be sure to follow all the instructions here, or you could get a false reading. I NOTICE: Too much or too little fluid can damage your transmission. Too much can mean that some of the fluid couldcome out and fall on hot engine a parts or exhaust system parts, starting fire. Be sure to get an accurate reading check your if you transmission fluid. 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. 6-20