1997 GMC Sonoma Owner's Manual - Page 75

Shifting from4LO to 4HI or 2HI To shift from 4LO to 4HI or 2H1, your vehicle must be stopped or moving less than 3 mph (4.8 k d h ) with the transmission in NEUTRAL (N) or the clutch pedal engaged. Thepreferred method for shifting out of 4LO is to have your vehicle moving 1 to 2 mph (1.6 to 3.2 k d h ) . Press and release the 4HI switch. You must wait for the 4HI indicatorlight to stop flashingand remain illuminated before shifting your transmission into gear or releasingthe clutch pedal. If the 4HI switch is pressed when your vehicle is in gear and/ormoving, the 4HI indicator lightwill flash for 30 seconds but not complete the shift unless the vehicle is moving slower than 3mph (4.8 k d h ) and the transmission is in NEUTRAL (N) or the clutch pedal engaged. On automatic transmission equipped vehicles, if your transfer casedoes not shift into 4H1, your transmission indicator switch may require adjustment.With your transmission in NEUTRAL (N), press and release the 4HI switch.While the 4HI indicator light is flashing, shift your transmission into PARK (P). Wait until the 4HI indicator light stays onbefore shifting your transmission into gear. This will get you into 4H1, but you should take your vehicle in for serviceto restore normal operation.