4x4 Trying to engage involuntary on GMC Sonoma 4.3

[Shrubbie]

My 4wd has been trying to engage on the highway, not enough to lock in, just enough for it to make a horrible grinding noise that forces me to the side of the road. Also at idle it makes a knocking sound similar to an engine knock but it's coming from the passenger side front wheel. Any clues to what it might be? I was thinking it was the actuator but what else could it be? Thanks.

[gmtech4]

My 4wd has been trying to engage on the highway, not enough to lock in, just enough for it to make a horrible grinding noise that forces me to the side of the road. Also at idle it makes a knocking sound similar to an engine knock but it's coming from the passenger side front wheel. Any clues to what it might be? I was thinking it was the actuator but what else could it be? Thanks.

I assume you have electric shift , it could a number of things but having the TCCM scanned is the first thing to do ,

 

Don't get into the shotgun parts at it thinking

[Shrubbie]

I think the tccm is fine, it's just the actuator doesn't have the power to keep the 4wd unlocked, and it's slipping a bit. I could be wrong though.

It goes in to 4wd just fine, it's coming out that's hard.

[gmtech4]

The TCCM stores codes on the whole system ,so I think you misunderstood what I said ,

 

You need a schematic and base electrical diagnosing skills to fix this , but hey , throw a part at it anyways ,

[Shrubbie]

Update: took it to the dealership I work at, the 4wd Vacuum pressure switch was bad. They replaced it for 70$ and it works like a charm.