4wheel drive will not engage, encoder?

Have it scanned for codes first as it can be a body module problem as well as a connection problem and or the transfer case module. A pro will problably have to do it due to the body module as auto parts can't get those codses

Ok we are going to pull codes to see what the codes may be present so we can see what it say's may be wrong with it. So the data link connector (DLC) is near the right side of the steering column. Now you need to make a jumper wire to go from the orange wire or term. number 13 at the DLC and ground. NOw turn key on engine off and watch the 4x4 light on the switch as it will flash codes to you. Now it will flash like a 1 pause 3 seconds and flash like a 3 meaning a 1 and a 3 as all transfer case DTC are single digit. So if you look at the diagram below it shows how it pauses as an example ok. After writing down all codes you will need to turn off the key and pull the 4x4 fuse and now turn the key on engine off 5 times this will clear all the codes from memory.
Now if you look at the graph below it shows what a code 2 will look like and what a code 1 and 3 will look like ok. Let me know what you find.

Ok did you do the reset procedure? If not do that just to see if it resets things. If nothing changes then we will have to test the stuff one item at a time.
Now we need to check voltages at TCCM harness (transfer case control module). With key on engine off you need to check for power at the following terminals. Refer to the diagram below ok. C8, C11, C12, C14, D14 and D15. Then check for resistance at C10 to ground it should be 2 ohms or less. If all it good then you will need to pull the 4x4 selector switch out and check for voltage at the pink wire at the switch. If all this is good then we will move to the next step. The diagram below will be needed for that too. Thanks and get back to me.

It is under the dash on the steering column support bracket. If this checks out then we will check the transfer case relay. Let me know what you find ok. Thanks.

If it is ignition power, then you need to start by checking fuses with a test light. Otherwise, look closely at the harness for breaks.

Roy

Hi CFerraro,
Just having power at the plug may not be good enough. There is also a ground side to the circuit that has to be good. It's still most likely that the actuator is not engaging the differential. That is what connects the drive shaft rotation into power at the wheels. Did you replace it with a new one or used? Also, do an ohms test or use a test light to be sure the ground is good in that circuit also. Let me know what you find out.
DWB

Hello,

I don't show an electric actuator for your year truck. Are you installing GM parts, many cheaper units will fail prematurely, the over size tires shouldn't cause the actuator to fail. When you remove the actuator can you inspect inside the transfer case to see if something is causing the problem, I have seen where the engagement fork will break causing the actuator to fail, the transfer case will need to be disassembled and repaired to fix the problem.

Let us know what you find

Best, Ken