Hey all,

I recently bought an '03 2500 HD Duramax 4x4 with 70k miles. It appears that the 4x4 isn't working. When I engage the ESOF it says that 4HI is engaged, and I verified that the actuator engages the front driveshaft, but my front wheels do not appear to be locked. I tested in sugar sand and only the rear tires spin.

I'm not an expert on how our 4x4 system works, but it does not appear to use locking hubs. Is there vaccum that is supposed to lock the hubs when I engage the ESOF, or are the hubs auto locked?

Any suggestions are appreciated.

Hey all,

I recently bought an '03 2500 HD Duramax 4x4 with 70k miles. It appears that the 4x4 isn't working. When I engage the ESOF it says that 4HI is engaged, and I verified that the actuator engages the front driveshaft, but my front wheels do not appear to be locked. I tested in sugar sand and only the rear tires spin.

I'm not an expert on how our 4x4 system works, but it does not appear to use locking hubs. Is there vaccum that is supposed to lock the hubs when I engage the ESOF, or are the hubs auto locked?

Any suggestions are appreciated.

Sounds like your tranfer case is ok if it is turning the front drive shaft. So it looks like a front diff problem. There is a magnetic actuator (plunger) in the front diff that is electrically controlled. It is located on the top passenger front side of the diff. Check all fuses first. If they are ok then unplug the actuator on the diff and remove it then plug it back into the wire. When you engage 4wd the plunger should move. If it doesn't move in and out while switching from 2 to 4wd, then there's your problem. The CV axles turn all the time. The front diff is locked interally by the actuator.

Thanks for the quick response!! The fuses check out OK and I can hear the front diff actuator "engage" when I hit the ESOF. What's the best way to remove the actuator to verify if the plunger is actually moving or not? Just a pair of channel locks? If it's not the actuator what else could it be?

Thanks for the quick response!! The fuses check out OK and I can hear the front diff actuator "engage" when I hit the ESOF. What's the best way to remove the actuator to verify if the plunger is actually moving or not? Just a pair of channel locks? If it's not the actuator what else could it be?
Yea channel locks or a big cresent wrench. It just threads out and dont forget the plastic washer on the threads when re-installing.

Well we pulled the actuator out and it moved correctly, but it still doesn't engage, any ideas where to look now?

BTW XNOTO made the post for me, its actually my truck he was just helping out.

Well we pulled the actuator out and it moved correctly, but it still doesn't engage, any ideas where to look now?

BTW XNOTO made the post for me, its actually my truck he was just helping out.
Are you sure the front drive shaft is turning? I would put the truck on 4 jackstands then try 4hi and 4lo and verify the transfer case is turning the front drive shaft. If it does not turn (with the truck is in the air and in 4hi) put the truck in neutral and spin one of the front wheels by hand. The front diff actuator should be engaged and turn the front drive shaft and the wheel on the other side should turn as well. This will tell you that it is a transfer case problem. If so, it will probably be the transfer case actuator.

Are you sure the front drive shaft is turning? I would put the truck on 4 jackstands then try 4hi and 4lo and verify the transfer case is turning the front drive shaft. If it does not turn (with the truck is in the air and in 4hi) put the truck in neutral and spin one of the front wheels by hand. The front diff actuator should be engaged and turn the front drive shaft and the wheel on the other side should turn as well. This will tell you that it is a transfer case problem. If so, it will probably be the transfer case actuator.

Well, I did notice that when removing the diff actuator, there appeared to be a very large amount of metal in the grease up there, looks like quicksilver.But when I stuck my finger in the fill hole to check the grease in there it looked milky. Im curious if that front diff is F-ed.


How well should the other wheel rotate when the front diff is engaged.

Could it be possible my transfer case is done due to a pump rub issue? Are there any tell tale signs of this?

Well, I did notice that when removing the diff actuator, there appeared to be a very large amount of metal in the grease up there, looks like quicksilver.But when I stuck my finger in the fill hole to check the grease in there it looked milky. Im curious if that front diff is F-ed.


How well should the other wheel rotate when the front diff is engaged.
The front diff should not have grease in it. It should have 75w-90 gear oil and if it's milky, then you have water in there. Sounds like a big problem. If you just bought the truck, did you buy it private or from a dealer. The previous owner may have known about the problem. I would go after him.

does the truck shift into 4-low?, Also when the truck is in 4wd, get underneath the truck(make sure it is in park and not running) and attempt to turn the front driveshaft.

Could it be possible my transfer case is done due to a pump rub issue? Are there any tell tale signs of this?
If your tranfer case has the pump rub issue, it will have a oil and dirt stain on the outside of the case leading from the pin hole back. Once all the oil is gone, it's a matter of time before it blows up, in which case it would not be drivable in 2wd.

The front diff should not have grease in it. It should have 75w-90 gear oil and if it's milky, then you have water in there. Sounds like a big problem. If you just bought the truck, did you buy it private or from a dealer. The previous owner may have known about the problem. I would go after him.

Bought it Private, and by grease I meant gear oil. Is there a way to determine if the transfercase is ok and only the front diff is bad?

does the truck shift into 4-low?, Also when the truck is in 4wd, get underneath the truck(make sure it is in park and not running) and attempt to turn the front driveshaft.

Its shifts into the low range but my front wheels still dont spin. Also, when I push the 4hi button it locks the drive shaft for the transfer case, if im in 2HI the shaft spins freely.

OK My guess is that your transfer case is good, however sounds like your front diff is the problem. The water in your front diff probably contributed to the condition. You said you could see metal and sludge on the actuator. You also said the other front wheel turned when you spun the opposite wheel by hand.
So I will say it is most likely that your pinion gear in the front diff is toothless. The guy that sold you the truck probably knew about the problem. I would go after him for the repair.
The front diff is easy to remove, I've done it several times on other trucks to change front axle seals.

unfortunatly it is a used truck, and it is buyer beware, so if you "go after" the other guy, legally you do not have a leg to stand on in "Most" States.

Good luck

Do you think I will be OK with just replacing the pinion gear set and flushing all of the gunk out of the housing?

Do you think I will be OK with just replacing the pinion gear set and flushing all of the gunk out of the housing?
First of all, have someone else confirm that this is indeed the problem!!
If so then replacing the pinion gear in place cannot be done.
You will have to remove the diff and split the case open and have a look. You might be better off finding a used diff complete and swap them out. Rebuilding the diff yourself is ok if your mechanically inclined and if you have the right instructions.
To remove the diff; remove skid plates. disconnect front drive shaft. . you can drain the oil now or later. Unplug wires to actuator and engaging sensor. Remove the 6 bolts holding the axle plates on each side to the diff plates. On the pass. side remove the to upper mounting bolts. Support the diff with a floor jack. On the drivers side lower, remove the bolt that goes through the rubber bushing. Diff should come out with some twisting and shaking. The diff plates are held in by a ring clip. Hit the plate firmly with a hammer away from the housing. It should pop out. Repeat for the other side. the case can be drained and split. It gets more complicated from here, try to find a service manual or the instructions.

Nice, Thanks man