2003 GMC Sonoma Owner's Manual - Page 285

How to Check Because this operation can be a little difficult, you may choose to have this done at the dealership service department. If you do it yourself, be sure to follow all the instructions here, or you could get a false reading on the dipstick. To get the right reading, the fluid should be at normal operating temperature, which is 180°F to 200°F (82°C to 93°C) Get the vehicle warmed up by driving about 15 miles (24 km) when outside temperatures are above50°F (10°C). If it's colder than 50°F (lO"C), drive the vehicle in THIRD (3) until the engine temperature gage moves and then remains steady for 10 minutes. A cold fluid check can be made after the vehicle has been sitting for eight hours or more with the engine off, but this is used only as a reference. Let the engine run at idle for five minutes if outside temperatures are 50°F (10°C) or more. If it's colder than 50°F (1OOC), you may have to idle the engine longer. Should the fluid level be low during this cold check, you must check the fluid hot before adding fluid. Checking the fluid hot will give you a more accurate reading of the fluid level. 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 system parts, 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. Wait at least 30 minutes before checking the transmission fluid level if you have been driving: When outside temperatures are above 90°F (32°C). At high speed for quite a while. In heavy traffic-especially in hot weather. While pulling a trailer. 5-22