OK here goes, I have a 2001 Jimmy 4x4 with the Auto 4wd (4 button)

Auto 4x4 works good
4 Hi works good.

About a year ago my front shaft went. I replaced it and we were also getting a error code for the encoder motor. So we replaced that as well. I tested it all seemed fine. After about a week 4 Lo stopped working again and I got the error "Can't up-shift transfer case". So we figured the encoder motor might be defective and I replaced it (I have kept the original). I also flushed the transfer case and replaced the fluid with GM. We used the truck for about a month then one day it would not shift into or out of 4 Lo if we were on the lawn only on the pavement. Then I got the error code again. 4 Hi and Auto still works, I'm fine if that is all I use.

So I was thinking what is the chance that a 3rd encoder motor has gone seems kinda of rare, but possible. What else could it be. Maybe the VSS on the transfer case. I removed it and it's not dirty, checked the resistance I think it was 1200. Should be good but is it??? I also noticed my cruise control does not work at the same time. so could a bad VSS cause the 4 Lo issues?? I'm thinking if I have a bad VSS the computer is not reading the speed correctly and since you have to almost be at a complete stop to engaged 4 LO, maybe the computer thinks the truck is moving??

Is this possible. Everything else works fine 4 Hi and Auto only 4 Lo and cruise don't work or do I have another bad encoder???

All parts in the front have been replace vac hose and all. Maybe the 4 buttons on the dash or the computer? What's your guess???

 

Anyone??

 

Are there any DTC's in memory?

If the VSS, or its circuits malfunction, it will set a DTC in memory. No DTC, no problem.

On your NV236 Auto 4WD: the TCCM analyzes the data from the front and rear prop shaft speed sensors. If the data is within the limits, it will allow a mode and or range shift. Yours is performing the mode shift which means both sensors are providing proper data. Could be an issue with the TCCM, encoder motor, dash switch, any of the circuits that connect it all together, or a problem inside the transfer case.

EDIT: You can remove the encoder motor and try to shift it manually, that would tell if the case can actually do a range shift.

 

This is the 3rd encoder motor, (defective), switch on axle replaced, actuator replaced up front. The only thing I can come up with are the dash buttons, TCCM (computer), VSS, and the Transfer case itself.