Q: 4 wheel drive on 2003 GMC Yukon XL 1500

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
The light by the 2 wheel drive was yellow and now it is red why?
(2) Answers
possible issue with rear drive shaft, transfer case, rear diff., rear wheel bearings. should bring in to shop for diagnostic run to confirm or dismiss. do visual inspection of rear wheels(looking for sign of blown seal, oil spattering around rim).