1999 GMC Sonoma Owner's Manual - Page 256

yellowblue If you do it yourself, be sure to follow all the instructions here, or you could get a false reading on the dipstick. Get the vehicle warmed up by driving about 15 miles (24 km) when outside temperatures are above 50_F (10_C). If it's colder than 50_F (10_C), drive the vehicle in THIRD (3) until the engine temperature gage moves and then remains steady for 10 minutes. Then follow the hot check procedures. Checking Transmission Fluid Cold A cold check is made after the vehicle has been sitting for eight hours or more with the engine off and 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 (10_C), you may have to idle the engine longer. Should the fluid level be low during a cold check, you must perform a hot check before adding fluid. This will give you a more accurate reading of the fluid level. Checking 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 parts or exhaust system parts, starting a fire. 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: D D D D 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. D Park your vehicle on a level place. Keep the engine running. in PARK (P). D With the parking brake applied, place the shift lever 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). 6-18