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Old 01-28-2015, 05:57 PM   #1
Redheaded DIY
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AWD not working

There is a lot of information about the rear wheels not driving due to the rear differential actuator not working. Since this is an expensive part, very few of us want to just throw money at the problem unless we are sure it is going to fix it. Don't get fooled since there may be more than one problem. I am working on a 2005 Montana SV6 with the Versatrak system. Come winter, it wasn't working and with this system, you won't know until you really need it. First I went to the GM dealer and paid for one hour of diagnostic time since my do-it-yourself code reader wouldn't read driveline codes. They found a right front wheel speed not registering and fixed the wires to that. Wheel bearings have also been known to be bad and since the sensor is part and parcel of the wheel bearing assembly, it is neither cheap nor easy. But it still didn't work so next I was told it was the actuator. Shame on me, I didn't ask if they read that code or if that was the only thing left that could be wrong. At this point I tried to find wiring diagrams, etc that would help me see what was or wasn’t happening. I found reference to the circuit for the actuator being a duty cycle type of value, again those of us under the shade tree will not be able to read that. What can be done is to drain the differential, then remove the actuator being sure to leave it plugged in. If you look at the actuator, you will see between the screen and the can, there is a piston that moves to open up the ports in the middle of the actuator. Now use the remote start (if so equipped) or have someone start the engine. When that is done, you should see that piston open up those ports. It doesn’t stay open, part of that duty cycle thing. The one I worked on would only buzz feebly and vibrate a little. Should you not feel or hear anything happening with the actuator, don’t bother ordering a new one until you find out why there is no signal back there. Remember, it is a duty cycle type signal and probably operates off of computer friendly 5 volts, so don’t try to activate it with 12 volts. Of course the solenoid part of the actuator could be totally fried. At any rate it is still a viable test piece. Did I mention to have the vehicle securely on jack stands since you will have to be under it? Now that one has determined the actuator is not working, that doesn’t mean replacing it will solve the problem. There are also gear rotor pumps, clutch packs and who knows what else that make the rear differential engage. After giving it some thought I decided to trick the system by removing the plunger. You will have to unscrew the filter to get at the tiny circlip that holds the piston on. Alternately, one could run a zip-tie through the ports or a length of mechanics wire to hold the piston partly open since getting the piston off is quite difficult. Make sure the assembly will go back into the housing without scratching any of the sealing surfaces. What you are doing is allowing the fluid to flow from one side of the diff to the other, essentially making it four-wheel drive. Re-fill the system with the proper oil GM part number 10-4058 (12378514). If you have already tried the drain and re-fill some folks recommend, save that fluid into a clean container and re-use it. Be sure to save the bottles it comes in to use for re-filling, makes it a whole lot easier. Also use a pump to keep from making a horribly expensive mess. A search of the internet should yield less expensive places to buy the fluid than GM, almost half as much. Now, find a suitably slick place to see if the rear wheels engage. You can confirm this with a helper or by opening the door and watching the rear wheel to see if it spins. Just don’t fall out and end up on the evening news. If the rear wheels now provide drive, you are about as sure as you can be that the actuator is the problem. If you have no rear wheel engagement, I would assume the clutch packs and pistons are the problem and that is very expensive to deal with as you no doubt have read in many forums by now. I think I would opt to put the old actuator in and just have a front wheel drive. If you need traction, put aggressive studless winter tires on it and it should be pretty good. All weather tires aren’t much good in anything more than a heavy rain in my experience. Another internet search should yield actuators for much less than the GM component and it will be the same thing since there are no after-market ones available, at least that I have found. For fear of giving erroneous information, I will not include the part number here since I have no idea what years and makes it fits. For my application, I was quoted around $450.00 at GM. I found one (had the same part # on the bag) for $238.00 and shipping. Your results could vary. Now with a new actuator in hand, don’t get too excited, there is still one more test. Plug it into the harness and start the engine again. You should see the piston retract for a few seconds and then close again. You may also notice that the piston flops back and forth in a good unit while in a bad unit it takes a lot of pressure to move it. This test will tell you if the wire harness is working and if the unit can work at all. Should you not see piston movement, I can’t help much there. I would assume it would be in the wiring harness or maybe the drive train cpu. Now put the new actuator in, re-fill with new oil. I found the oil I had filled it with was already nearly as dirty as the original oil. I have read many variations of the procedure to drive in a left hand circle for 5 minutes and then a right hand circle for 5 minutes. To keep from getting dizzy, one could do a figure 8 for 10 minutes after all this is forcing the pumps and what not to push oil through the system and purge air from it. I also noticed the much talked about moan which I had never heard before. Frankly, it was hard to hear and it sort of had a rhythm similar to what he actuator does. Unless this noise doesn’t go away or is very loud, I wouldn’t worry about it. If it’s really horrible and wasn’t present before, one might consider removing the functioning actuator and putting the old one in. It depends on how much you depend on the AWD system. I am of the opinion this is more of a drive-ability system compared to a true go-for-it off road system. I wouldn’t recommend it for really gnarly driveways or roads. Also bear in mind a lot of folks recommend changing that fluid every year! And that’s just the differential, there is also a transfer case lurking up there somewhere. I hope this helps and bear in mind, modern vehicles are incredibly complex machines. There are a few things you can still do yourself if you’re willing to roll around under a vehicle and search the web for ideas.
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Old 01-30-2015, 08:33 AM   #2
Tech II
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Re: AWD not working

Yes, these vehicles use the Versatrak system, and you must use Versatrak fluid, which is expensive.....

There are three problems that I have seen with this vehicle....

One is the "moan" sound when taking a turn......for some people, they think it is coming from the front, but it is actually coming from the rear.....can verify by making turns, and having someone listen standing outside the vehicle.....

The procedure is to remove the fluid, and refill with new Versatrak fluid.....then find an open area, and drive in a circle one way for 5 minutes, and then in the opposite direction for 5 minutes......usually the moan will dissipate or be gone before the full 10 minutes, but do it completely......then remove the the fluid again, and refill with new Versatrak fluid......DO NOT REUSE ANY FLUID.....

The second problem is, you will see AWD Disabled in the DIC.......the USUAL fix is the actuator, as previously mentioned......however, as also mentioned, the harness and the signal have to be confirmed first......

The third problem, which was on the earliest models, was a fluid leak between the transmission case and the transmission.....this was Dextron III or VI(which ever was used at the time), not Versatrak fluid.....this was a costly fix also....
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