Auto 4wd function

Rex3 · January 14, 2022

Hello, I have a 1999 sierra, when I put it in auto 4wd it acts like it is in 4hi. I do not have any cel, or service lights on. All the lights on the push button 4wd switch work. Any idea where I need to start looking as to why it is doing this. Thanks in advance and thanks for the add to the group.

Jworks · January 14, 2022

If I'm understanding this correctly its because it is in 4Hi and thats why its acting that way. IF the truck senses the road conditions need it to be then it will be in 4Hi. If its in snow, mud, or senses any traction issue it will be in 4Hi. If its a hard dry surface it should be in 2Hi. If its a hard dry surface and it feels that way, something is wrong.

If I'm wrong on this someone feel free to correct me.

Edited January 14, 2022 by Jworks

newdude · January 14, 2022

1 hour ago, Rex3 said:

Hello, I have a 1999 sierra, when I put it in auto 4wd it acts like it is in 4hi. I do not have any cel, or service lights on. All the lights on the push button 4wd switch work. Any idea where I need to start looking as to why it is doing this. Thanks in advance and thanks for the add to the group.

Are you saying that in AUTO you are getting binding when turning in the front end like its in 4HI?

Rex3 · January 14, 2022

Yes that's exactly whats going on.

Rex3 · January 14, 2022

I was on dry hard surface and put it 4auto and front axle was binding like it was in 4hi. I had a 1999 Tahoe and used the 4 auto and never felt like that.

Sharpz · January 15, 2022

While in auto 4x4 there isnt power persay to the front axles but they are on demand or activated in case you are in a situation that say you are cruising highway speeds, come to a hill that might be a bit slippery, the auto 4x4 detects that you are losing grip, and automatically puts power to the front axle, where as if you didnt have this feature activated you would need to push the button (which you should do anyway) for 4 hi. It is sort of like a clutch. A slight moan is humming is completely normal, at least its been for all of my trucks when I have been in auto 4 or 4 hi.

rbdjr · January 15, 2022

If its a auto 4wd mode - Make sure you have the correct fluid in the tranfercase, sometimes you can do a fluid change and then 50 miles later change again, if condition still present you will need to adjust the cluct pack in the transfercase, with either new discs and plates and or selective plate.

Edited January 15, 2022 by rbdjr

Supreme Pizza · January 15, 2022

Auto is not much more than a convenience. You dont really need it.

Work around:

Don't use auto. Just drive it in 2 or 4 wheel drive.

newdude · January 15, 2022

16 hours ago, Rex3 said:

I was on dry hard surface and put it 4auto and front axle was binding like it was in 4hi. I had a 1999 Tahoe and used the 4 auto and never felt like that.

Gotcha. You could start simple, get 2 quarts of fresh GM AutoTrak II Fluid (the blue stuff) and drain out what's in the case. I suppose there is a possibility that old or wrong fluid could be making the clutches send power to the front when it shouldn't.

The more likely scenarios would be that the encoder motor (transfer case actuator) isn't shifting the transfer case correctly and is only giving you 4HI. There could be an issue with the transfer case control module, but you'd be seeing codes with that.

You are getting driving symptoms of being in 4HI, so it sounds like the front axle is actuating properly, so that leads me to think your issue is in the transfer case.

Edited January 15, 2022 by newdude

Rex3 · January 15, 2022

17 minutes ago, newdude said:

Gotcha. You could start simple, get 2 quarts of fresh GM AutoTrak II Fluid (the blue stuff) and drain out what's in the case. I suppose there is a possibility that old or wrong fluid could be making the clutches send power to the front when it shouldn't.

The more likely scenarios would be that the encoder motor (transfer case actuator) isn't shifting the transfer case correctly and is only giving you 4HI. There could be an issue with the transfer case control module, but you'd be seeing codes with that.

You are getting driving symptoms of being in 4HI, so it sounds like the front axle is actuating properly, so that leads me to think your issue is in the transfer case.

I will give that a try. I did have an error on the abs side, bad wheel speed sensor i changed that and cleared the codes and so far so good. I thought I read if there was an error on the abs it could case issues with the 4wd, was hoping that this was the case but it wasn't. I like the auto mode for winter driving. Thanks for your insight.