GM Service Manual Online
For 1990-2009 cars only
  1. The range shifts are the shifts between the HI and the LO ranges.
  2. • 2HI to 4LO
    • 4HI to 4LO
    • 4LO to 4HI
    • 4LO to 2HI
  3. A range shift can only be made with the automatic transmission in neutral or with the manual transmission clutch fully depressed. The shift occurs when the vehicle speed is below three miles per hour.
  4. Whenever a shift into 4LO is initiated, the 4LO select switch button blinks. The 4LO select switch button will continue to blink until the shift is completed mechanically or until 30 seconds elapses. The 4LO select switch button must be on and not blinking prior to shifting the transmission into gear or releasing the clutch pedal.

If a range shift is initiated when the transmission is engaged or the vehicle speed is above 3 mph, the 4LO select switch button will blink for 30 seconds and no range shift actually occurs, the TCCM will default and position the transfer case into 4HI.