Finally decided to diagnose my 4x4 issue… uh oh…

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LM7Tahoe01

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So… I’ve known for a while that my 4x4 doesn’t work. I finally got around to trying to figure out why…

The button lights up the way it should, there’s no “service 4wd” light, and I can hear the encoder motor on the t-case.

Next I jacked up a front wheel and hit the 4HI button and confirmed that the t-case locks in but the axle doesn’t.

Ok, maybe it’s the actuator, those are a known issue. I crawled under the front end and had my son hit the 4HI button and… I could feel the actuator running… Uh oh. Looks like I’m on the hunt for a front axle… unless the actuator is running but not actually pushing the fork over? I suppose the next step is to drain the oil and check for sparkles or chunks…
 

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What year, is it the AUTO transfer case? Recommend putting some vehicle info in your signature.

The encoder motor is on the transfer case. It may still not be switching modes correctly but usually that will throw a code, but not always.

Couple of things to check: all four wheels on jackstands, off the ground, in 4HI does the front propshaft spin? If so, and the front wheels still don't turn, there is likely something wrong with the front diff actuator or its circuit. Generally that one won't throw a code.

You can test the front diff actuator, see YouTube for various ways to verify the circuit and operation. Unscrew it and with key on, switch to 4HI, and it should extend within a second. They can get lazy or nonfunctioning. The dirty ground for that circuit is on the driver's side body mount (which is on the frame), behind the left front tire, and below the driver's door hinge.

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A Tech 2 would help solve this issue.
 
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LM7Tahoe01

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Thanks for the quick reply!

2001 Tahoe, 5.3, “Auto” t-case. I will have to update my signature…

Encoder is the one on the T-case, actuator is on the axle.

I am 100% sure that the case is locking in. I can spin the front driveshaft in 2HI with one front wheel off the ground (KOEO) and I can’t spin the front driveshaft same conditions in 4HI. I can feel the actuator doing something, but haven’t removed it from the axle yet to see if it actually extends… maybe I’ll try that next…
 

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Might have to disconnect the electrical connector to be able to unscrew it and there might be a few drops of diff fluid, but not much. Reconnect the electrical and let it hang by the wires, then switch into 4HI. No need to have the truck running, just KOEO.
 
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LM7Tahoe01

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Well, I tried to pull the actuator out today, but I forgot about First Compressions 9.5:1- what GM has put together let no man take apart…

I tried all kinds of pliers, and even pulled the skid plate off to get a straight shot, but it won’t budge…
 

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