Torque on demand

It is not the best thing to do but it is okay to drive it until you have a chance to repair it.

A couple common issues with them is the front wiring harness, it gets near the exhaust and the insulation melts. Another is the speed sensors fail.

These issues will set codes that can be read with the proper scan tool or using the method listed below.

If you want to pull the codes yourself it is possible to do, you need a simple piece of wire and a pen and paper.

First, find the DLC connector, it will be under the dash with a cover over it and look like the first image below. It can mounted right side up (wide section up) or upside down as it likely is in your truck.

Take the piece of wire, strip the ends and twist them tight. (Or cheat and use a small paperclip bent into a U shape) You want to connect the number 8 pin (transfer case module) and the number 4 pin (ground).
Number 8 is the pin directly opposite the pin with the red circle. Pin 4 is in the same row just count backwards from pin 8.

Now for the hard part. Turn on the key and you should see the same check light you are seeing now start flashing.
As it flashes it will tell you any codes stored.
To read the codes you count the flashes

Flash pause Flash Flash would be code 12 and indicates it is now in diagnostic mode.

That will flash three times.
Flash pause flash flash, long pause flash pause flash flash, long pause flash pause flash flash.

Now start counting, each code will flash 3 times. So if you see
flash flash pause flash flash flash flash, long pause flash flash pause flash flash flash flash, long pause flash flash pause flash flash flash flash.
You would read that as Code 24 - Rear speed sensor open or shorted to ground.

When it finishes flashing any stored codes it will begin the cycle again starting with 12. When you see 12 again you can turn off the key and stop counting.

These are the codes you could see and what they mean.

12 - Normal Operation.
13 - Reference Circuit Shorted To Ground.
14 - Front Speed Sensor Open Or Shorted.
15 - Reference Circuit Shorted To Power.
16 - Front Speed Sensor Has No Running Speed Pulse.
21 - TP Sensor Has Faulty Voltage, Shorted Or Open.
24 - Rear Speed Sensor Open Or Shorted.
26 - Electromagnetic Coil Shorted To Ground.
27 - Front Or Rear Speed Sensor Has No Pulse.
28 - Axle Disconnect Output and Axle Switch Output Abnormal.
31 - Electromagnetic Coil Disconnected Or Shorted.
32 - Axle Disconnect Output Shorted Or Disconnected.
33 - Axle Disconnect Output Circuit Shorted To Ground.
23, 36, 37, 38 - TOD ECU Failure.

Once you have read the codes and written them down you can clear them if you wish, if the problem is constant the light will come back on and flash at you just like it is.

To clear the codes, you put the wire back into the same two pins.
Apply the parking brake or put a block in front and back of a wheel to keep the truck from moving. Then shift the 4WD (HI-LO) lever into neutral.
Turn on the key and step on the brake pedal five times in five seconds.
If you are in neutral and have the pins connected you should see all of the TOD indicator light each time you step on the pedal.

Then come back here and post the code(s) you find and we can sort out what is wrong and you can decide how to proceed.

Most of those codes suggest a wiring problem. Either a damaged harness or connector that is shorting the wiring. I would start there, looking at the rear wiring harness to the axle for damage or chaffed wires.