4WD HI/LO light blinking

[96CK]

Alright,

I've dug and dug but can't seem to find something similar to this one. I've even tried using good ol Google.

I have a 1996 Z71 with a 5.7 Vortec and pushbutton 4wd.

When I push the button for 4HI it stays blinking, 4LO I get a solid light and you can hear the clunk plus when you pull forward it really pulls (4LO).
I had my son engage/disengage 4HI while I was under the truck (truck off, key forward) and I can hear the actuator engaging.
I'm able to rotate the driveshaft prior to engagement, but once it engages I can't rotate it.
It seems that it's engaged but the 4HI light won't stop blinking.

Is it possible that despite engaging, the actuator is either A - partially engaging or B - has a faulty sensor of some sort that prevents it from communicating full engagement?
Both of which I would suppose would require actuator replacement?

I don't want to just toss parts at my truck, last time I did that I got a dent........

 

[RichLo]

You can take the actuator out and visually see if it is moving. That wont tell you how strong it is but if it moves and the 4hi light stays lit then it may just be weak.

My 2001 Blazer sometimes has funny push button 4wd similar to your problem. 4lo always works but sometimes switching between 4hi and 2hi I have to leave it in whatever one is blinking, shut it down for 2 sec then start back up and it'll stay lit and stay in that mode.

 

[96CK]

So, despite it actually engaging the prop shaft, it might not be engaging "enough" for it to recognize that it's been engaged and the light stays blinking?

That's the part that's confounding, I lay under the truck, hear everything engage, can't rotate the prop shaft, but the light stays blinking.

I mean..... parts house is 5 mins away, and if it doesn't fix it I can always return it.... I hate doing that tho.

 

[Supercharged111]

I'd start by pulling TCCM codes, that's easy. But if the shaft stops turning that tells me the t-case goes into 4, but if the light is flashing that means either the encoder motor isn't telling the TCCM that that is the case or the front actuator isn't actuating. But you said it grabs 4lo, so I'd start by pulling TCCM codes. Hopefully a more savvy member will chime in with a link.

 

[RichLo]

Is it actually in 4-lo or is it just the transfer case making it 2-lo. Even if the front diff isnt engaged the driveshaft will be tied to the rear driveshaft when the t-case switches.

Can you get on gravel or grass and see skid marks from the front?

Either way, I think your safe to assume the actuator is bad at this point. They are known failure points in these trucks.

 

[Macs Garage]

I have my transfer case apart right now and the shift motor rotates a plate which hits a sensor when engaged. Could it not be turning enough or a bad sensor switch.