4WD Mystery

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Kaivbech

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Hi, folks.
First of all, thank you for all your knowledge. I’ve been a long time reader, here is my first post (I might be posting this in the wrong section, but here it goes!)

My 99 K2500 Suburban with the auto 4WD-button in the panel have two issues:

- Will not come out of 4WD hi
- When the 4WD light is on, I am still able to turn the front wheels with the front end raised up, so it does not ACTUALLY have 4WD

Here are my diagnostics
- If I pull fuse number two in the inner fuse box, the front diff disengages
- If I insert the fuse back in and then pull the 6 pin transfer case connector, the front diff disengages and I can Push the 2nd button, and the light switches from 4WD to 2wd

My questions are
1. Do I have a bad transfer case switch?
2. Can a bad transfer case switch cause not issues; no actual 4WD and front diff not disengaging?

Any help is appreciated!
 

stutaeng

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Yeah, it does sound like switch is bad. I wonder if there's a way to test it?

Could be the transfer case actuator that's bad? I've got a 04 2500 suburban (bought as a project) with the NP263(edited) and the harness for the actuator was severed. I removed the actuator and spliced the wires, but it still didn't work.

I don't really know about 4wd drivetrains, just learning. My other truck (K3500) has that old school shift lever. :rolleyes:
 
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DonYukon

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Just to clarify , when your switch says its in 4hi your not getting power to your front CV shaft?

Does the truck have autotrac? (easy way to know you will have a button that says "AUTO 4WD" as a 99 Id assume it would but im not sure about the K2500s never owned one.

You could have a couple of issues.

Do you have a "service 4wd Light on?

If you do check the TCCM (Transfer Case Control Module)
Or
VSS (Variable Speed sensors) I think on the NP246 for a 1500 there is 2

If you dont have a Service 4wd indicator check for continuity on these

Encoder motor - This one is on the transfer case and controls the transfer case input
Front diff Acuator - Located on the front diff Passenger side
Switch in dash - ... on dash lol
 

Nad_Yvalhosert

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My '99 GMC Jimmy was stuck in Auto 4x4 a while back. The t-case was in 2wd, but the actuator engaged the front differential. Thing would steer hard around corners, but not lock up.
I changed the encoder motor and everything returned to correct operation.
 
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