Jump to content

Auto 4wd function

Rex3
 Share

Recommended Posts

Rex3 Enthusiast

Rex3

Posted
Posted

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 Enthusiast

Jworks

Posted
Posted (edited)

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 by Jworks
newdude Senior Enthusiast

newdude

Posted
Posted
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 Enthusiast

Rex3

Posted
  • Author
Posted

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 Enthusiast

Sharpz

Posted
Posted

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 Enthusiast

rbdjr

Posted
Posted (edited)

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 by rbdjr
newdude Senior Enthusiast

newdude

Posted
Posted (edited)
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 by newdude
Rex3 Enthusiast

Rex3

Posted
  • Author
Posted
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. 

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing

  • Latest Articles

  • Posts

    • jgaudet99
      Tire psi

      By jgaudet99 · Posted

      Thanks for all that information, I might purchase one and see if it will work for me, if not they may let me return it! Yes for sure the tires are definitely within limit for my truck empty, and when I do tow I'll definitely make sure to raise the rear psi for the amount of weight that's going to be on it.
    • Chuck FB
      Tire psi

      By Chuck FB · Posted

      Yes exactly, more and more these days people/companies are afraid of liability issues so its easier just to say no rather than risk putting their neck on the line.    I will say with the Autel unit or when I used it last year on my truck, it wasn't like I could choose the 2025 model year or even the 2024 model year as that option was not there to manipulate the placard pressures but had to go back to 2023 or there abouts and then it showed up as an option, odd but that was how the software was then and I can't say one way or the other now as they throw out updates every so often. I still would talk to your tire dealer though to start with and they may do it for nothing but also they may have a comment on a better unit to purchase. All I know is that one of the large tire shops in my area happens to use these Autel units for their use and set them up to use the wifi and all of that jazz for constant updating because each tire tech has one handed to them by the shop but I just plugged it into my laptop to update it and yes if one is bought it has to be registered so you can get the link to do updates and then the unit has to be updated before its even used. I am not at all techy so it took me a bit but anyway just a heads up for anything you buy, most likely it will need to be connected to a computer to access the internet to have it updated to the latest software version before you can put it to use.   If your truck is near empty, those tire pressures you listed are a very safe upper range pressures to carry the weight, both the front and rear as I know they could be run lower yet with an empty truck. And if its a trailer and not some motorcycle your going to strap onto the front of your truck on a rack, you shouldn't have a need to inflate your front tires if your at 55 front already, its the rear ones that would need more air if you have much hitch weight. 
    • jgaudet99
      Tire psi

      By jgaudet99 · Posted

      Thank you, I'll check that Autel scanner out and see if it will work for me! Ya I can see GM's point of view if they lower the psi set value for someone and the person sell's the truck and the new owner puts the factory tires back on then their could be liability issues cause the psi warning light wasn't coming on when the tires were under inflated for towing their load and then it might be able to be traced back to GM lowering it.
    • Chuck FB
      Tire psi

      By Chuck FB · Posted

      I had a similar but different response when I talked to the service manager where I bought my truck in that he said GM corporate won't allow them to lower the placard pressure setting as they would get their hand slapped but that of course they have the ability to make that change. His suggestion was simply go to a tire dealer or third party shop that is willing to reset the pressures lower. However I chose to buy a tpms tool and partly based off of this very forum as it had been proven to work on the 2024 model ( Global B system ) and while I could have paid lots for a full two way diag tool, I didn't want to spend that much and bought the recommended Autel TS 508 and it will reprogram the 2025 model and assume it should do the 2026 as well. However the tool is rather proprietary to reprogramming Autel tpms sensors so that is a function I will never use, where as a real two way scanner would have many uses but also have yearly subscriptions etc where this 508 is free updates for as long as they put updates out for the unit. In any event it worked to lower the placard pressures and I often use it to adjust my actual tire pressures although will check with a mechanical gauge as well sometimes just to make sure that tires tpms sensor isn't lying to me.    My suggestion is either buy a tool that you know will work to adjust the system or start out by getting the tire shop you bought your tires from to reset your truck and if after that you still want a unit to do it yourself, get one at that point. 
    • jgaudet99
      Tire psi

      By jgaudet99 · Posted

      Here is an image of a quick Google search about these tires on my truck and it's exactly same psi recommendation the Toyo tires company gave me!    I'm not looking for anyone else recommended psi or anything, I'm just looking to see if anyone knew a way to get rid of the factory low psi warning light, because I'm not running high psi and ruining my tires when I'm not towing! 

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...