Transfer case in 99 GMC Suburban

check vacuum line and the actuator under the battery tray to make sure its working properly

The selector drive mtor mounted on the transfer case had alot of problems with water getting into the circuit board and also the mtoro drive getting stuck. At the dealership I have replaced hundreds of these over the years.

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If you have push button transfer case,likely shift motor or controls.If the transfer case has a shifter,and it moves freely,likely internal problem

You definitely need to have it serviced & checked out...The service 4WD indicator read across my screen, but I did not have serviced...Eventually, I heard a grinding noise & because I didn't have it serviced when I took it in, it was found that the transfer case had no tranfer case fluid at all...This damaged the transfer case which had to be replaced (used transfer case-$400.00)....The transfer case is part of your transmission...The shape mine was in could have broke my transmission...Have it taken care off before it gets too bad...You must use only GMC Transfer Case Fluid

If it's a manual case ( pull stick ) then it's dexron III automatic trans fluid , if it's automatic ( push button ) then use GM part # 12378396

the transfer case module is bad it is bolted to transfer case above front drive shaft

reverse is blown,tranny job!

If it has auto 4x4. which will have 4 push buttons on the dash it will take auto trac fluid that you will need to get at your local GM dealer. A regular transfer case will take Automatic transmission fluid.

maybe another 4x4 transmission or transfer case?