2003 GMC Envoy Owner's Manual - Page 410

100,000 Miles (166 000 km) 0 V8 Engine Only: Inspect spark plug wires. 0 150,000 Miles (240000 km) U Drain, flush and refill cooling system (or every 60 months since last service, whichever occurs first). See Engine Coolant on page 5-24 for what to use, Inspect hoses. Clean radiator] condenser] pressure cap and neck. Pressure test the cooling system and pressure cap. An Emission Control Service. 0 Inspect engine accessory drive belt. An Emission 0 0 CI 0 An Emission Control Service. Replace spark plugs. An Emission Control Service. Change automatic transmission fluid and filter if the vehicle is mainly driven under one or more these of conditions: - 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 haven't used yourvehicle under severe service conditions listed previously and, therefore, haven't changed yourautomatic transmission fluid, change both the fluid and filter Automatic Transfer Case Only: Change transfer case fluid. V8 Engine Only: Inspect Positive Crankcase Ventilation (PCV) valve. An Emission Control Service. Control Service. 6-9