Auto 4x4 Trouble

[Searsy]

I have a 2003 GMC Sierra. When I put the vehicle into Automatic 4X4 it sounds and feels as though the truck is actually in 4 Hi. It is my understanding from having owned a 99 Jimmy in the past that the vehicle should actually be in 2 wheel drive until the computer senses a "slip" in the rear and at that point, the computer will send power and lock all four wheels in drive. Can someone please tell me whether I'm right or wrong? When I turn in Auto 4 especially at low speeds (such as parking), the front wheels "chuck" as though it is in 4 Hi/Lo.

 

I would appreciate it if someone can explain to me the sequence of events once the auto 4x4 button has been pressed i.e. function of modules, actuators, diff etc.

 

Thanks in advance......

[DofD]

It does sound like when you select auto 4 wheel it is going into 4x4. Try putting it into 4hi to see if the driving characteristics are the same. If they are that is a pretty good confirmation that auto 4 wheel is going into 4hi.

 

The problem is probably electrical in nature. Have you tried using a scanner to see if there any diagnostic codes being generated?

[pwall]

First, welcome to GM-Trucks.com!

 

In regards to the Auto4WD, it's my understand that the front hubs are activated, just not the transfer case...or perhaps the other way around.

Thus, having your truck in Auto4WD would not be the same 'feel' as in 2WD.

[Green_Monster]

First, welcome to GM-Trucks.com!

 

In regards to the Auto4WD, it's my understand that the front hubs are activated, just not the transfer case...or perhaps the other way around.

Thus, having your truck in Auto4WD would not be the same 'feel' as in 2WD.

 

+1 Front wheels are engaged with no power going to them until there is slip. From what I know clutch packs in the T-case are what engage when in auto4wd, instead of gears when in 4hi.