1999 GMC Sonoma Owner's Manual - Page 314

yellowblue Scheduled Maintenance Short Trip/City Intervals Every 100,000 Miles (166 000 km): Spark Plug Wire Inspection. Spark Plug Replacement. 4.3L V6 Engine Only: Positive Crankcase Ventilation (PCV) Valve Inspection. Every 150,000 Miles (240 000 km): Cooling System Service (or every 60 months, whichever occurs first). These intervals only summarize maintenance services. Be sure to follow the complete scheduled maintenance on the following pages. Long Trip/Highway Definition Follow this scheduled maintenance only if none of the conditions from the Short Trip/City Scheduled Maintenance is true. Do not use this schedule if the vehicle is used for trailer towing, driven in a dusty area or used off paved roads. Use the Short Trip/City schedule for these conditions. Driving a vehicle with a fully warmed engine under highway conditions causes engine oil to break down slower. 7-6