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Discussion Starter #1 (Edited)
OK - educate me!

My friends '05 OBL (205K miles) has an issue in the drivetrain that I have not been able to trace to either the front or rear diffs and axles - all seem good there. However, I'm wondering about the center diff ( viscous?)

The car exhibits a lot of tire dragging when the steering is almost at full lock, and sometimes now seems to exhibit a bit of extra drag when going straight ( he says - I haven't driven it on the road yet myself). At times, when backing up with the wheels turned near full lock, with only mild throttle, the car will move for a few feet, then stop moving, and will then move again with more throttle, but rather reluctantly.

You can hear the tires dragging a bit on the slightly sandy shop parking lot when turning sharp. The tires are all good, the same circumference, and at the proper pressures (he has Firestone maintain the tires for him).

I believe that if the center diff is f'd up, it could be the cause of this extra drag.

Opinions?
 

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Discussion Starter #3
Its the 4eat ( OBL - Outback Limited model).

I assume that this car also has the usual means of inserting a fuse to turn it into FWD only ( didn't think of this while the car was here!). If put in FWD mode, would you expect that to eliminate the issue if the problem indeed is the center diff? I called him on this a minute ago and left him a message about trying that to see if it made a difference.
 

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Discussion Starter #4
Hmmm.... Just read on the Forester forum that the center diff issue could be that the transfer solenoid has failed, or that both the solenoid AND the diff have failed.


If the solenoid has failed - which, if the information is correct, would cause the clutches to lock up solid - then I would expect that there would be no change in the problem symptoms if the FWD fuse is inserted.

Opinions again?
 

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If the solenoid has failed - which, if the information is correct, would cause the clutches to lock up solid - then I would expect that there would be no change in the problem symptoms if the FWD fuse is inserted.
The 4AT AWD doesn't have a center differential with viscous coupler; instead it's a multi-plate wet clutch hydraulically controlled by a duty solenoid and a spool valve ("transfer valve") on the valve body.

With the 2005 4AT, if the solenoid or wiring to it fails (e.g., open circuit) it's default position causes the hydraulic fluid to be drained from behind the clutch piston, so no pressure on the clutches. But these faults should lead to a trouble code.

Certainly worth trying the AWD disabling fuse; the socket for it is in the main fuse box in engine compartment. If it relieves the problem, then it is due to incorrect pressure on the clutch. There's been cases where, without any duty-cycle signal the solenoid remains off, but as soon as any duty cycle is applied, for some reason it goes to full on. It could be due to deposits in the solenoid or transfer valve, leading them to stick open. Sometimes, repeated drain-and-fills of the ATF can clear this type of problem if, e.g., the solenoid or transfer valve is sticking because of accumulated deposits.
 

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Discussion Starter #6
OK. So "failure" of the valve - eg - zero voltage, or failure of the solenoid itself - - causes the clutches to be fully disengaged, which would eliminate any drive to the rear. That would seem to make no sense, since inserting the fuse to energize the solenoid also disengages the clutches. Unless I am misunderstanding the clutch action, of course.

If the valve is stuck "open", is that the position that applies pressure to the clutches?
 

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That would seem to make no sense, since inserting the fuse to energize the solenoid also disengages the clutches.
Inserting the fuse fuse doesn't "energize" the solenoid. The fuse simply acts as a switch that, when "off" (i.e., fuse out) signals the TCM to control the solenoid normally for AWD function, and when "on" (fuse in), tells the TCM to disable the AWD. The real control is programmed in the TCM.
 

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Discussion Starter #8 (Edited)
Got it. Makes sense now! Thanks. :) Unfortunately, I've read elsewhere that inserting the fuse turns the solenoid on, and can lead to its demise, since (according to the writer) it is not a constant duty solenoid. However, my'96 Legacy Brighton with the 4EAT has been run with the fuse installed for the last 60K miles, so that - at least for how that car is set up - shows that to not be the case. Maybe they were referring to those models with the viscous coupling differential only.

Hopefully my friend will get the chance to try inserting the fuse today, and we can sort things from there.

And I correct that both the solenoid and the valve are accessible when the trans pan is removed?

One last question (hopefully!) - is this the same setup that I have in my '01 and '03 OB Limiteds?
 

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Unfortunately, I've read elsewhere that inserting the fuse turns the solenoid on, and can lead to its demise, since (according to the writer) it is not a constant duty solenoid.
Yes, in the pre-2005 4AT, inserting the fuse signals the TCM to disable the AWD. In those years, the solenoid worked in reverse of what the 2005 does; with a low duty cycle, the clutch pressure is high, and with a high duty cycle, the clutch has less pressure. In the pre-2005, if the connection to the solenoid fails (bad connector contact, broken wire, open circuit solenoid coil), and there's no power to the solenoid, the AWD clutch will be applied fully.

The possibility of affecting the solenodi with the fuse in permanently is a concern, but is probably very rare, and, if the solenoid, or transfer valve, were to fail somehow, it would probably be attributed to a different cause. As with the other valve body solenoids and valves, they are moving most of the time (when the car is running). That helps prevent the build up of deposits that can cause sticking or blockage. But when held in one position for an indefinite time, there isn't this cleaning action.

And I correct that both the solenoid and the valve are accessible when the trans pan is removed?
The AWD solenoid is accessible from underneath, but the transfer valve (a spool valve) is built into the valve body, and as I recall, is accessed through one side. It might be possible to access it with the valve body in place, but that might be awkward. If it comes to having to get to it, probably just as well to remove the unit so that it can be more easily worked on the bench.
 

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Discussion Starter #10 (Edited)
Thanks. If we end up having to dive into it, I'll have to find a decent set of drawings. I know that there is a link to the digital shop manuals somewhere on this forum, so that is probably my best bet. Not really looking forward to having to do that - at my age, crawling under cars is no longer much fun or very easy! :)

So my Gen 2's work the opposite of the '05 - the fuse makes the computer energize the solenoid constantly.

Excuse me for rewriting what you stated above, but I just want to make sure that I am reading what you wrote correctly (and the same for others in this predicament) and understand the solenoid function correctly.

_

So, in the 2005, when the fuse is inserted. it tells the computer to disengage the solenoid by not sending a signal to it, allowing the solenoid to shift to its default position, in turn shifting the valve to depressurize the clutches. If that is correct, then the "duty" of the solenoid is of no concern. The causes of this issue then could be any of or a combination of the following:

1 - The solenoid is for some reason constantly getting a signal, energizing it and pressurizing the clutches. Possible that the computer is doing this, but highly unlikely, I would expect. If this were the case (a constant signal), inserting the fuse should interrupt that signal, unless the computer is really f'd up in its programming, or whatever it energizes to send power to the solenoid is stuck in the "send a signal" position ( does it use a relay to power the solenoid?)

2 - The solenoid is physically stuck in the energized position even with no signal going to it, so inserting the fuse will not change anything.

3 - The valve is stuck in the energized position, and stays there even if the solenoid is in the default position. That would indicate to me that whatever shifts the valve to the "clutch disengaged" position is not working properly (I have no idea what does that on this design, but it would have to be either a physical connection to the solenoid, a return spring, or a hydraulic pressure return).

4 - The clutches themselves are stuck together.

If the valve is stuck but the solenoid is good and the signals to it are correct - indicated as a possibility if inserting the fuse changes nothing - would the addition of some Seafoam possibly unstick it?
 

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What are the chances of the clutches themselves being f'd up?
There have been earlier generation, high mileage, cases of the clutch plates having worn grooves in the clutch drums, causing the plates to bind, and yes, lead to similar torque bind symptoms. But I don't recall any that appeared in the 2005+.

Start with seeing the effect of installing the fuse. Also, try a few simple drain-and-fills of the ATF, with a bit of driving in between each. Leave the solenoid/valve body to the end of the list.

Note: Subaru does not list or supply any parts for the valve body; it's replaced as a unit whenever there's a fault. However, I believe there are aftermarket AWD solenoids available, but possibly not any others, or other parts, such as the spool valves, springs, etc.
 

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Discussion Starter #12
Yup - doing the fuse is first. Haven't heard back from him yet about whether he's done that or not. I'm also awaiting back an answer on when the trans fluid was last changed, so a drain and fill may also happen soon. His two jobs are delivering pizzas on the weekends and running parts between all of the Autozone stores in the area during the week, so he gets a lot of driving in every day.

Unfortunately looking at subaruonlineparts, there isn't much available for replacement parts for that transmission. They do list a "control module" for $500+, which I suspect is the complete solenoid control assembly. Hopefully we don't have to go that deep into this thing - if so, I'll do a lot of looking for replacement solenoids in the aftermarket. If the problem is in the valvebody, I would attempt to repair it first ( did a fair amount of that decades ago in a CNC maintenance job) - he unfortunately is in a bit of a financial pickle, so that sort of expense is out of the question.

Thanks for your help and patience on this thing!
 

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Discussion Starter #13
If it comes down to having to replace the valve body or the control module, it would probably be cheapest to find another 4EAT in a junkyard for a couple hundred bucks, and swap out the parts. If that ends up being the case, how do you predetermine that those parts are compatible to swap? Do you know of a list of those particular parts and what year versions of the 4EAT they are in?
 

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Do you know of a list of those particular parts and what year versions of the 4EAT they are in?
It's unlikely (but, of course, not impossible) that the Transmission Control Module is at fault. If you have a scanner that can access the Subaru data stream at the OBD connector (e.g., Romraider), the TCM signal to the solenoid can be easily checked to see if the duty cycle is in the proper range under different driving condition. Another way is to measure the voltage on the wire going to the solenoid. Being a duty cycle signal, it will be less than battery voltage, and vary with driving conditions.

The valve body (AWD aspects) could be faulty, as discussed earlier. I don't recall any significant changes to the 4AT valve body during the 2005-9 generation, but I could have missed that. Could check the part numbers by year/model/engine/transmission for the valve body at Subaru Parts Online from Subaru of America. (Pre-2005 is not compatible, and the 4AT was discontinued with 2010+.

I think a lot depends on what happens with the fuse installed (incidentally, when it is installed, the "AWD" warning light in the instrument panel should turn on.)
 

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Discussion Starter #15
Thanks - have been thinking about getting Romraider for a while, so now maybe is finally the time to do so. As to the control module model, I did see on one advertisement for new ones on ebay that the newer design was phased in over the '05-'06 model years, but there was no mention of in which car models. Hopefully we won't need a new one.

While we are on the subject of transmissions and the control module, I have an issue with my '03 OBL, in that if it is called to downshift from locked-up 4th to 3rd - like in flooring it to pass someone - there is a slight hesitiation and then 3rd comes in with an awfully hard bang. If I understand the system correctly, I suspect that the fluid for the 3rd clutches is draining back out of the 3rd passageway, causing the big pressure spike that engages the clutches late and hard relative to the increasing rpms. Is the fluid held in the passages with some sort of pressure sensative check valve that could be faulty? This sort of hard downshift can't be doing the clutches or anything else in the drivetrain any good.

This transmission WAS driven for who knows how long with the fluid level extremely low before I bought the car, so who knows what sort of damage was done in the meantime.
 

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have been thinking about getting Romraider for a while, so now maybe is finally the time to do so.
Romraider is the way to go for engine and AT data, unless you can access much more expensive equipment that can commmunicate with the Subaru system.

As to the control module model, I did see on one advertisement for new ones on ebay that the newer design was phased in over the '05-'06 model years,
Not sure what it's referring to; the valve body, or the Transmission Control Module. Certainly, there were changes between 2004 and 2005, and it's possible there were some carryovers of 2004 versions into 2005, and then updated for 2006. They would have to be more specific.

I suspect that the fluid for the 3rd clutches is draining back out of the 3rd passageway, causing the big pressure spike that engages the clutches late and hard relative to the increasing rpms.
What happens if while driving in 4th, in lock-up, but not too fast, rather than flooring it, the gear selector is used to downshift? Does it do the same thing?

Sometimes rough shifting isn't due to the transmission; it's engine-related. Engine torque is normally managed during a shift to avoid shock.

There might be other threads/posts in the forum dealing with the same issue.
 

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Discussion Starter #17
Not sure what it's referring to; the valve body, or the Transmission Control Module. Certainly, there were changes between 2004 and 2005, and it's possible there were some carryovers of 2004 versions into 2005, and then updated for 2006. They would have to be more specific.


What happens if while driving in 4th, in lock-up, but not too fast, rather than flooring it, the gear selector is used to downshift? Does it do the same thing?

Sometimes rough shifting isn't due to the transmission; it's engine-related. Engine torque is normally managed during a shift to avoid shock.

There might be other threads/posts in the forum dealing with the same issue.
They are referring to the Transmission Control Module.

Have thought about trying the manual downshift, but haven't tried it yet. I would expect that the shift would be smooth, regardless of any drainback issues, depending on how the throttle was applied - it the expected rev rise is matched, there should be no shock, but if the throttle was floored at the same time as the shifter is moved, I would expect the shock to still occur. Hopefully will get the chance to experiment soon.

Have looked for other threads on this, and asked about the problem last winter in the Gen 2 forum, but found nothing and no replies at the time, unfortunately.
 

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Discussion Starter #18
OK. Some progress. He just stopped by on one of his runs to drop off a case of super-discounted Prestone deicer (Autozone is trying to get rid of all their stock as they change over to Rain-X instead), so we inserted the fuse, and in a simple run around the parking lot test, he says that it is a lot better. He'll call back in a couple hours after some more deliveries to let me know if it is better out on the road.

If inserting the fuse fixed the problem. that seems to tell me that everything inside the transmission is working properly - the solenoid is returning to its default position correctly, the valve is shifting correctly, and the clutches are not welded together. So the question is : What could be the problem? It would seem that the solenoid is getting a constant signal that it should not be getting, or a much stronger signal than it should be getting.

Does the ecu feed the solenoid directly?

Or does it control a relay that in turn controls the solenoid? If it does that, then my suspicions would first be directed at the relay being stuck "ON". Is that even possible with these relays?
 

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Does the ecu feed the solenoid directly?
Yes. There's a connection from the TCM to the solenoid. (It's the TCM, not the ECM, that controls the solenoids.)

As noted earlier, the TCM sends a duty cycle signal to the solenoid coil. This is a rapidly switching on/off (high/low) voltage. The On time can vary. The longer the voltage is on/high, the longer the solenoid remains in the activated position, and more fluid can pass through it. When the On time is reduced, the solenoid is open for less time.

The longer the solenoid is open, the higher the pressure applied to the AWD multi-plate clutch. But the solenoid doesn't do this directly. Instead, the fluid that passes through the solenoid is used to control the related AWD transfer (spool) valve. It's the transfer valve that controls the passage of high capacity hydraulic pressure from the pump to the clutch.

Both the solenoid and valve are spring loaded. A weak spring could lead to the valve opening more than it should, applying more pressure on the clutch than is intended at a particular duty cycle.

Or, if the valve bore has deposits in it, once it opens, it might tend to stick open (or not close as quickly as it should) rather than respond to the small changes in the "pilot" control pressure from the solenoid due to changing duty cycle. When the fuse is installed, and the solenoid is off, the total absence of pilot pressure for more than just an instant might then allow the valve to return to it's default position, thereby releasing the clutch.

What't the history of ATF maintenance over the 15 years? As mentioned earlier, this might be a case where repeated changes of the fluid might help.
 

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Discussion Starter #20 (Edited)
What't the history of ATF maintenance over the 15 years? As mentioned earlier, this might be a case where repeated changes of the fluid might help.
I asked him about that, and he has no idea since he has owned the car for only a couple of years. I checked the color of the trans oil while he was here, and it was still mostly red, but just enough off of the color I expected to make it suspicious. I told him to get 5 gallons of fluid and we would go through the multiple drain and fills as soon as he has a day that we can do that. Hopefully that will fix the issue.

Would adding some Seafoam in the meantime possibly help?

Interesting the control method, in that it is hydraulic pressure that controls the valve, instead of the solenoid directly pushing on the valve - would never have thought of that. Will have to see if I can find something that explains how the TCM decides what level of signal is sent.
 
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