Problems with 4X4 not working?

Yes you can replace the actuator yourself here is a diagram to help you get the job done. The actuator encoder as they call it is on the side of the transfer case.

Check out the diagrams (Below)

Please let us know if you need anything else to get the problem fixed.

Cheers

First 1998 is not very old.

Second, that should have shift on the fly in it. That means it has an inter axle disconnect in it and you can shift between two High and four High without stopping. You pull the lever or push the button and the transfer case will shift into four high and the front drive shaft starts moving. At the same time there is a switch that activates the front axle interlock. This moves a collar that locks the right hand axle together and you are now in four wheel.

To shift into four low is different. You cannot shift into that on the fly. You have to stop, put the transmission into neutral, shift into four low and then shift into drive/reverse. Reverse the process to go back to four high or two high.

Have it scanned for codes auto parts can do for free

You cannot jump anything to read codes a scanner would be needed for this. Put old tcm back in if you have it and check to see if power is going to encoder motor on tcase. Check fuses where shown in pic and also check to see if encoder motor is getting power and working. Finally check switch on tcase where arrow is to see if that is working.

Do you have a manual shift 4wd or electric?

Make sure you are getting power to the actuator. Check the actuator on the front axle.

I attached a wiring schematic for the transfer case electrical. Take a look and see if it helps.

Unfortunately you 'll have to have it scanned for codes, any garage can do which are cheaper than the dealer. It may be the encoder motor on tcase or a wiring issue but it needs to be scanned first to see what code it is.