2004 GMC Envoy Owner's Manual - Page 330

Automatic Transmission Fluid When to Check and Change A good time to check your automatic transmission fluid level is when the engine oil is changed. Change both the fluid and filter every 50,000 miles (83 000 km) if the vehicle is mainly driven under one or more of these conditions: 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 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: • In heavy city traffic where the outside temperature regularly reaches 90°F (32°C) or higher. • In hilly or mountainous terrain. • When doing frequent trailer towing. • Uses such as found in taxi, police or delivery service. If you do not use your vehicle under any of these conditions, change the fluid and filter every 100,000 miles (166 000 km). 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. 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 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. How to Check Because this operation can be a little difficult, you may choose to have this done at the dealership service department. 5-22