Need help! 4wheel drive not working

[Sean Coombs]

Ok total newby to the forum. I own a 2007 GMC Sierra 2500 HD. 4 wheel drive quit working last month. Figured it was the actuator as I could feel the t case engage in 4lo but axles wouldn't lock in. Replaced the actuator and still nothing. Ive read there is a fuse under the hood but not sure which one it is. Any help guidance would be appreciated.

 

Thanks

Sean

[davester]

Unscrew the actuator, and then plug it into the harness and see if it goes in/out as you switch between 2 and 4wd.

 

With the actuator unscrewed, and shifted into 4wd (you may have to move the truck a bit to complete the shift), you should not be able to rotate the front driveshaft and the actuator should be sticking out.  If this is the case, then shift back into 2wd, reinstall the actuator and plug it in, shift back into 4wd, lift one front wheel and try to spin it.  If it doesn't spin, the system is working.  If it does spin, then most likely the locking gear or passenger side stub axle is broken.

[newdude]

GM's diag:
 

Quote

 

 

 

- Raise the vehicle. Refer to Lifting and Jacking the Vehicle.

 

- Remove the actuator motor. Refer to Front Drive Axle Actuator Replacement.

- Using a brass drift, apply pressure to the clutch fork.

- Turn the right wheel to align the clutch gears.

- While turning the right wheel, does the left wheel turn in the opposite direction?

 

 

So, if you apply pressure and the wheel turns in the opposite direction, you've got an electrical issue, be it a bad actuator, transfer case control switch, transfer case module, bad fuse, etc.

 

If you apply pressure and the wheel does NOT spin in the opposite direction, you have a mechanical failure in the axle.  That failure would most likely be in the tube housing that the actuator sits in, aka. the inner shaft housing. 

 

I've crudely circled that housing in the pic below.

 

 

Numbers 5, 6, 7, 8, 9, 10 and 11 would be prime suspects.  Also, 37 is a possibility, but not as likely I don't think.  16 is the actuator.   

Edited December 19, 2019 by newdude

[davester]

Note, the above post assumes both front wheels are off the ground and are free to rotate.  If you just lift just one of the wheels, then substitute "can't rotate" for "wheel turns in the opposite direction",  and "can rotate" for "wheel does NOT spin in the opposite direction".

 

And I believe that parts #1, #8, and #37 are the primary bits that physically fail...

Edited December 19, 2019 by davester

[Dnt]

There is a reset procedure for the transaxle clutch pack, you can probably find it on the internet easily.  I am not 100% sure but I think it goes something like this. Set parking brake turn key switch on and put gear selector in neutral. Turn key switch to off position for 60 seconds. Turn key switch to on position and place 4whl selector in 2hi for at least 10 seconds, after 10 seconds rotate the 4whl selector clockwise past 4hl low and hold all the way to the right for at least 30 seconds. You should hear the actuator cycle. Place the selector back into 2whl Hi position and restart the truck and you should have full function now.