1998 GMC Sonoma Owner's Manual - Page 269

With the parking brake applied, place the shift lever in PARK (P). With your foot on the brake pedal, move the shift lever through each gear range, pausing for about three seconds in eachrange. Then, position the shift lever in PARK (P). Let the enginerun at idle for three minutes or more. Then, without shutting off the engine, follow these steps: 1. Flip the handle up and-then pull out the dipstickand wipe it with a clean rag orpaper towel. 3. Check both sides of the dipstick, and read the lower level. The fluid level must be in the COLD area fora cold check or in the HOT area orcross-hatched area for a hot check. 4. If the fluid level is the acceptable range, push the in dipstick back in all the way; then flip the handle down to lock the dipstick in place. 2. Push it back in all the way, wait three seconds and then pull itback out again. 6-19