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4WD On Demand From 4EAT!

351K views 609 replies 127 participants last post by  davidaga 
#1 ·
MountainBiker (I think) posted in the old subaruforester.com forums about a method by which you could flip a switch to essentially lock the center diff when needed. At the time I didn't have the service manuals and couldn't figure out how to do the mod. Now I have the manuals, and can't find the old post because the archives are apparently gone.

So, I'm hoping someone (MountainBiker, you still here?) can shed some light so I can perform this little mod. It would have been very nice to have this winter, which is almost over now, but there's always next year.

If anyone needs the relevant parts of the service manual, let me know, I have them in PDF format and would be happy to share the parts necessary to get this thing going.

Thanks!

Zhe Wiz
 
#53 ·
XT Different?

Well, I can see why the mod didn't work on my car now, but I'm afraid it doesn't get me any closer to a solution.

I tested my white w/green stripe wire, pin 4 on plug B56. Ignition on in all tests. Here are the results:

Park, Throttle Closed: 0.00 volts (So far, so good)
Drive, Throttle Closed: 2.0 volts (Should Be 5-7 volts)
ANY GEAR, Throttle Fully Open: 5.6 volts (Should Be < .5 volts)
FWD fuse installed: 0.00 volts, all gears (Should Be > 8.5 volts)

Now I have absolutely no idea what to do. It is clear, however, that my car does not act at all like the cars of those who have done this mod successfully. Either something really changed in the way the AWD system works in 2004, or the XT is very different, or my car is not acting as it should, or I have the wrong wire.

Bottom line is, someone who knows a lot more than me about schematics/electronics will have to figure this one out. I'm at a loss as to how to get this mod to work on my car.

Jack
 
#54 ·
Hmmm - my manual in the "Engine Section Transmission Module I/O Signal" around Pg 432 lists "Transfer Duty Solenoid" as B54 pin 15. See if you can find a similar reference in your manual.

But then later on it says B54 pin 6 for non-turbo and then also refers to B54 pin 6 for the turbo model as well.:icon_confused:

Based on the tests pin 15 was correct for mine.
 
#55 · (Edited)
Kevin said:
Hmmm - my manual in the "Engine Section Transmission Module I/O Signal" around Pg 432 lists "Transfer Duty Solenoid" as B54 pin 15. See if you can find a similar reference in your manual.
OK, now we're definitely getting somewhere. I found the same section of the manual for my turbo Forester and it has uncovered some interesting facts. First of all, I do indeed have the correct pin. The "Transfer duty solenoid" (also referred to as the "AWD Duty Solenoid" in other sections of the manual) is on pin 4 of connector B56. So the wire location is definitely different (same color though!) from the non-turbo. Oddly, but importantly, the voltage expected on this pin is VERY different from the voltage expected on the non-turbo! It is almost backwards for some reason. When voltage goes UP on the TURBO version, the system apparently gets "closer" to 4WD. When voltage goes UP on the NON-TURBO version the system gets closer to FRONT wheel drive. Why would Subaru have changed it on the Turbo version? Seems odd.

According to the manual I'm supposed to see "more than 10.5 volts" in first gear, throttle fully open on the turbo version. (A more "4WD" situation) The NON-TURBO expects to see < .5 volts under the same test conditions. Another interesting fact is that the TURBO version has only 2.5-4 ohms of resistance vs. the 10-17 for the NON-TURBO.

These facts do help to explain the odd (or so it seemed at the time) results I obtained when trying the mod. When I cut voltage to the Transfer solenoid, I was essentially experiencing FWD instead of 4WD and the above implies that is what one would expect to see on the TURBO car. The fact that I gave 15-16 ohms of resistance to that wire, explains why I got a check engine light even though the car was running when I flipped the switch.

OK, that's all well and good, but what does this mean exactly? Does it mean that in order to force 4WD on the turbo model that I need to send a power signal to the solenoid while putting a 2 - 4.5 ohm resistor on the other side of that wire? That's what it looks like to me, but I'm not an electrician, I'm a programmer. And I discovered a long time ago that programming logic doesn't always work for electricity. :) And I'm not going to try it unless someone who knows more than I do thinks that I won't blow anything up by trying.

Which leads me to another question. Is it possible I've already messed up something? Could putting those 15-16 ohm resistors on that wire from the tranny computer cause permanent damage? Sure hope not, but my Check Engine light is still on... [EDIT: As of this morning (6 July 2006), my Check Engine light is OUT, so it appears that I did NOT do any permanent damage]

So am I the ONLY turbo owner trying to perform this mod? Perhaps the "mod it" types who bought the turbo also bought the 5 speed and aren't interested? Oh well.

Thanks for your continued help in trying to figure out how to get this working on the XT! I think we're getting close. Sure hope this helps someone else out in the future.

Jack

Relevant section of the manual is attached (See Page 2)
 

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#56 ·
Alright, looks like no one is willing to go out on a limb and say whether or not my idea will work, SOOOOO, I'll have to show the schematics to a couple of friends of mine (if I can ever pin them down long enough!) and see what they say. If it looks good in theory, I'll give it a shot and see what happens.

Jack
 
#60 ·
Zhe Wiz said:
Alright, looks like no one is willing to go out on a limb and say whether or not my idea will work, SOOOOO, I'll have to show the schematics to a couple of friends of mine (if I can ever pin them down long enough!) and see what they say. If it looks good in theory, I'll give it a shot and see what happens.

Jack
Sorry, I missed your above post somehow. Yes, it looks like your model is somehow using more voltage for more lock up of the transfer clutch. Looks like you would just need to supply full battery voltage when you want it locked up. Try it out. Don't worry about the resistors, because all they do is prevent a MIL from the TCM.
 
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#61 ·
MountainBiker said:
Sorry, I missed your above post somehow. Yes, it looks like your model is somehow using more voltage for more lock up of the transfer clutch. Looks like you would just need to supply full battery voltage when you want it locked up. Try it out. Don't worry about the resistors, because all they do is prevent a MIL from the TCM.
Hey, no problem! Thanks for having a look. I'll go ahead and give the mod a shot either tonight or over the weekend. Wish me luck!

I'll post back the results, once this is straightened out and tested, I think a summary post here and maybe at scoobymods.com is in order?

Thanks,

Jack
 
#62 ·
Success!!!!

It worked! It worked! Wooo Hooo!! :)

I just got back from the test drive in my XT, and sending 12v to the solenoid side of the white/green wire absolutely did the trick! I also put 2, 20 watt, 8 ohm resistors in parallel and connected those to the other (Trans Computer) side of the white green wire when my switch is on.

Worked perfectly, and no check engine code was thrown. Absolutely awesome!

Thanks to SeaComms for waking me and this thread up again, Kevin and MB for helping me think through the problem, and MB for giving me the courage to "be the first" as far as turbo owners go. :)

I'll try to steal MB's and SeaComms' diagrams and re-do them for the turbo version for future reference.

Thanks again for all your help.

Jack Z
 
#421 ·
It worked! It worked! Wooo Hooo!! :)

I just got back from the test drive in my XT, and sending 12v to the solenoid side of the white/green wire absolutely did the trick! I also put 2, 20 watt, 8 ohm resistors in parallel and connected those to the other (Trans Computer) side of the white green wire when my switch is on.

Worked perfectly, and no check engine code was thrown. Absolutely awesome!

Thanks to SeaComms for waking me and this thread up again, Kevin and MB for helping me think through the problem, and MB for giving me the courage to "be the first" as far as turbo owners go. :)

I'll try to steal MB's and SeaComms' diagrams and re-do them for the turbo version for future reference.

Thanks again for all your help.

Jack Z
Hi, I have stumbled onto another interesting issue with my 04 XT 4EAT.... pin 4 on B56 shows 2.5v throttle closed .. then up to 4v at around 50% throttle... then to .5 past 50% throttle... Anyone run into this?

Thanks,
Jeff
 
#64 · (Edited)
Summary

OK, I'm uploading all of the diagrams for going 4WD on-demand. One set is based on SeaComms' method (essentially, he uses a relay with a remote switch - which is the version I used,) the other is based on MountainBiker's (he uses only a DPDT switch, no relay).

MY DRAWINGS ARE COMPLETE THIEVERY OF THEIRS. I have stolen them and added the instructions for the turbo Forester. The rest of the credit goes to them, not me.

Please have a look and make sure I didn't do anything stupid when I translated your work MB & SeaComms, also if you want me to type credits or change something, by all means let me know. I'm not trying to take credit for anything here, I just want to make sure if a turbo owner stumbles upon this, they know what to do as well.

Hope this helps someone with a Turbo Forester some day!

Jack Z
 

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#65 ·
Hey Jack, I don't really care about credit. In fact, I only came up with the successful implementation after being inspired by Jody Reid at SubaXtreme!

As far as I can tell, Jody offered this for sale before there was anyone doing the mod on their own and posting it on the internet. By the time I got around to placing my order with SubaXtreme, they had stopped selling it! So I had to purchase the genuine Subaru manual. Once I saw where to tap in the switch, I searched all the internet forums I could find to glean some info. The idea of the resistors for preventing the MIL came from people that had purchased Jody's switch!

Now to the schematic. I would not presume that the pin and connector is the same for everyone, which is why I left it off the schematic. There should probably be a note saying something like "typically Pin 15...."

And lastly, I want to repeat my disclaimer:

DISCLAIMER:
While I believe this mod to be safe when used correctly, use it at your own risk. If any thing harmful happens to you, your car, your possessions, innocent bystanders
, or passengers, don't blame me, this forum, or anyone else but yourself!
 
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#66 ·
MountainBiker said:
Now to the schematic. I wonder about your wire color notation. It has been too long for me to remember, but typically, when I say Green/White, I put it in that order because the wire is mostly green, with a white stripe. This is the convention of every service manual I've ever looked at. You have the order reversed, was that on purpose?

Additionally, I would not presume that the pin and connector is the same for everyone, which is why I left it off the schematic. There should probably be a note saying something like "typically Pin 15...."
MB: As for the color change, indeed that was on purpose. I thought you had made a mistake when you made your schematic. Bad assumption on my part! The wire in my car is white with a green stripe! I'm curious about SeaComms' car now - is his white with a green stripe or green with a white stripe? I *think* I saw him call it a white/green wire which is why I assumed you had switched them unintentionally. Curious. Will have to change that section of the schmatic as well, since it obviously varies from year to year or model to model.

Your pin/connector suggestion is a good one also. I'll "loosen" that section up a bit and will note that it is pin 4 of B56 for 2004 XT's and recommend referring to the shop manual for your particular car for exact location and color of the wire.

Thanks for the suggestions and for clearing up the chain of ideas.

Jack
 
#67 ·
Not so fast! Now that you say you did it on purpose, I'm thinking I made a mistake, I'll take a look.
.
.
.
Yes, I found an old post where I called it a "white wire with a green stripe", so your schematic is correct! I've edited my above post. I should probably go back and alter my old schematics I've posted too.
 
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#68 ·
MB: Excellent, looks like the color, at least, is consistent among our relatively small sampling no matter which model or year.

I'll tweak the schematics per your other suggestions and put up a new copy in the next couple days, looks like I can leave the color alone, though I'll probably still advise that it be double-checked.

Thanks for all of your help!

Jack
 
#69 ·
I just want to provide an update on this mod. I have had no issues, and I've used this since January 2005. However, some people over on USMB.org have reported some issues and serious damage to their transmissions!

As far as I can tell, those that have had problems didn't use any resistors as shown in my schematic, they just directly wired a switch to interrupt the signal to the duty C solenoid. Some may also have used twisted wire connections rather than soldering.

So I must state once again, do this mod at your own risk, and don't exceed your electrical and mechanical abilities and know-how!
 
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#71 ·
Me too pleeeeeeease! :icon_biggrin:

I also have not had any problem and followed MB's schematic - used parallel resistors but same result. I also only use it when absolutely necessary and then only for short periods of time (except on loose sand).

If my transmission gets into any trouble it will be from waiting for the torque convertor to heat up enough to grab when climbing really steep slopes. (no more than 15 seconds at a time though)
 
#86 ·
This is something I would like to look into as well, when my warranty runs out. I have a couple of questions though.

1) SeaComms was able to switch his Forester to FWD only (although it was by mistake). Would it be feasible to utilize this as a way to increase MPG?

2) How worried are you about leaving the the transfer locked up? One post mentioned only using it 15 seconds at a time. How about instead of a toggle, use a push button, so you have to hold it in to keep things locked? I guess is you are bouncing around off road that might be difficult.
 
#77 ·
Thanks Kevin - have been lurking for a short while, and at OffroadSubarus

I found the link to here from OffroadSubarus, and it's the first place I've found actual diagrams of the circuit. I'm pretty sure I could build it with a little help from a mate, but just wasn't sure which way would be the way to go.

FYI, I'm a programmer by trade, and a bit of a computer geek by choice, and I have some rudimentary understanding of electronics.
 
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