2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 485

How to Check Automatic Transmission Fluid Because this operation can be a little difficult, you may choose to have this done at the dealer 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. Notice: Too much or too little fluid can damage the transmission. Too much can mean that some of the fluid could come out and fall on hot engine parts or exhaust system parts, starting a fire. Too little fluid could cause the transmission to overheat. Be sure to get an accurate reading if checking the transmission fluid. Wait at least 30 minutes before checking the transmission fluid level if you have been driving: . To get the right reading, the fluid should be at normal operating temperature, which is 82°C to 93°C (180°F to 200°F). Get the vehicle warmed up by driving about 24 km (15 miles) when outside temperatures are above 10°C (50°F). If it is colder than 10°C (50°F), drive the vehicle in 3 (Third) until the engine temperature gauge 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 10°C (50°F) or more. If it is colder than 10°C (50°F), 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. When outside temperatures are above 32°C (90°F). At high speed for quite a while. In heavy traffic - especially in hot weather. While pulling a trailer. ... 6-25