Wife always wanted SUV, found sweet looking 99 Bravada in great shape and did my due diligence on it. Bought it on premise that I'd still be ahead if I had to put several thousand into it.

Of course, it had some crowhop on slow turn and the 'Service AWD light' came on intermittently almost immed. after I signed.

I've changed the TC fluid per GM TSM with the proper lube. The crowhop improved greatly by doing that.
But once that was done the AWD service light comes on constantly after starting any trip.

A good shop that I trust and with a good name told me to just ignore it, the truck drove normally and the binding feel on turn-while-backing remains, though I had the rear end serviced and inspected.
Problem being he called in his 4WD specialist and guy pulling code said it was just a flaky sensor and nothing to be concerned about. Why do I not feel comforted by THAT!! The shop owner is a family friend and has great rep but I'd rather find the problem.

Told him that and he said... "well, if you pay me enough I'll find it for you. OTOH, you know cars pretty well and how to research, so why dont you find the troublemaker and I'll fix it cheap"

Any ideas? BTW wife loves the Bravada, and I do too.. except for the nagging service light.

 

Pulling the code should indicate which sensor went bad. Once you have the code, just look it up here and then replace that sensor. I know on the 99 models you can replace the sensor individually.

 

The sensors can be tested like any speed sensor, but spinning the relevant shafts can be somewhat problematic. I put the whole vehicle up on suitable jack stands and have someone inside put the vehicle into drive while I monitor the output. You are looking for the output to be >250mV-AC from all of the speed sensors on the t-case.

The encoder motor can be tested as well, but that doesn't sound like your problem. There really isn't much to the NV136 encoder. No brake (as in the NV236 encoder), no position sensor (as in the NV236 & NV233 encoders); just a DC motor with two wires coming off it that drives through 3 planetary type reductions & another 2 step (3 gear) reduction. To test the actuator, test the cold resistance across the motor windings. Then apply +12V & ground to the motor (it should whirr to life or possibly not) and then retest the resistance. If it goes to infinite resistance, the motor is smoked and needs to be replaced.

 

Good Info... thanks guys! I have a bookmark folder on the car and this link is going into it. I'm quite sure it's a degraded sensor on one of the two, because I have some experience on them in a non-automotive environment and the progressive symptoms point exactly to that.

Heck... I even have a plan B in case the transfer case goes all the way out. It becomes a 2WD. Thanks to Chris015.

Saying, as I did in the OP, that we would still be ahead if we had to pour another couple thousand into it, changes somewhat once the thing is part of the normal day-day life. We didnt buy it because of 4wd.
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Updated 9/13

Gadzooks!!! The problem seems to be solved for now. Who fixed it and how was it fixed.. ???

Well, the old lady did it. Road crew working on highway she takes to work left one of those huge steel coverplates covering who knows what.. and didnt bevel up to it very well. She said the 'Service AWD' light went out right after she drove over it with a jarring bump.
And now there is no indication of 'binding up' while backing and turning.

IMO this points to yet another bad splice pack.. probably a ground splice, I'll have to look it up.