2003 GMC Sonoma Owner's Manual - Page 288

Manual Transmission Fluid When to Check A good time to have it checked is when the engine oii is changed. However, the fluid in your manual transmission doesn't require changing. Then, follow these steps: How to Check Because this operation can be a little difficult, you may choose to have this done at your GM dealership service department. If you do it yourself, be sure to follow all the instructions here, or you could get a false reading. 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 part or exhaust systemparts, starting a fire. Too little fluid could cause the transmission to overheat. 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 transmission case. 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. 5-25