4WD only engages in 4-LOW

[89Suburban]

I recently tested out my 4WD in a gravel lot. I switched it into 4-HI. Drove slowly and turned the wheel one way or the other to feel if the front wheels were engaging and dragging and they weren't. So I put it in neutral and shifted into 4-LOW and put it in gear and the front axle was engaged and doing it's thing. This has me scratching my head. Truck runs and drives fine, I am not getting any warning lights from the dash or control knob when attempting these tests. Not sure why the front axle is only engaging in LOW and not HI. Thanks for any insight.

 

[swathdiver]

I recently tested out my 4WD in a gravel lot. I switched it into 4-HI. Drove slowly and turned the wheel one way or the other to feel if the front wheels were engaging and dragging and they weren't. So I put it in neutral and shifted into 4-LOW and put it in gear and the front axle was engaged and doing it's thing. This has me scratching my head. Truck runs and drives fine, I am not getting any warning lights from the dash or control knob when attempting these tests. Not sure why the front axle is only engaging in LOW and not HI. Thanks for any insight.

Check for internal trouble codes and then run some diagnostics with your Tech-2.

 

[89Suburban]

Check for internal trouble codes and then run some diagnostics with your Tech-2.

I have neither sir.

 

[swathdiver]

I have neither sir.

No internal codes? And when you roll the knob to engage 4HI, it lights up and stays there but doesn't actually engage?

 

[wjburken]

I have neither sir.

Are you certain that the 4HI is not engaging or are you just going by feel? My 2007 Silverado didn't buck when it was in 4HI so to make sure it engaged, I went to a gravel lot and from a stand still went hammer down to break the tires loose momentarily and saw that 4HI did in fact engage as I had the tell tale marks from front and back sets of tires. You could also put the truck up on jack stands and see if the front tires engage.

 

[89Suburban]

No internal codes? And when you roll the knob to engage 4HI, it lights up and stays there but doesn't actually engage?

Using my pocket scanner reveals no codes. The lighted knob thing, I thought so but I can't remember now, I will re-test tonight to make sure and report back.

Are you certain that the 4HI is not engaging or are you just going by feel? My 2007 Silverado didn't buck when it was in 4HI so to make sure it engaged, I went to a gravel lot and from a stand still went hammer down to break the tires loose momentarily and saw that 4HI did in fact engage as I had the tell tale marks from front and back sets of tires. You could also put the truck up on jack stands and see if the front tires engage.

Just going by feel. I'm afraid to hammer down on it, she ain't no spring chicken anymore, I don't want to break anything lol.

 

[Fless]

Gotta have a scanner that can pull transfer case codes, so you may not be seeing them.

Check out the post below and the link inside it. You can test that front diff actuator to make sure it's getting commanded to engage in the 4hi mode. I also assume that you have an Auto mode, but when that's selected the diff actuator won't engage until the speed sensors indicate back tire spin (which you can do with all four corners on jack stands). A Tech 2 would make your troubleshooting easier, it sure did for me.

https://www.tahoeyukonforum.com/threads/4wd-not-engaged-when-indicated.116196/#post-1402816

 

[captain63]

Had exact issue, it wound up being the two grounds underneath the drivers door at body mounts, removed bolts, cleaned ground wires and reinstalled.

 

[Fless]

Had exact issue, it wound up being the two grounds underneath the drivers door at body mounts, removed bolts, cleaned ground wires and reinstalled.

One of those grounds goes to the front diff actuator.

 

[captain63]

Yep