dashton

Here's the latest: Finally got around to checking the connections and signals from both speed sensors. Both of them check out perfectly to the TCU. And the TCU must be reading them because I cut both wires and got errors for both sensors. So before I forget how to do it, here's the procedure to check the signals: VSS1 (in the transmission tailshaft) Check for AC (alternating current) voltage in connector B44 at the TCU. This is the small connector in the middle, and it's a black wire in position 12. You'll want to verify this with the wiring diagrams from Josh's website. Hook up the voltmeter to the wire (I cut the wire and put the voltmeter in series) and drive off. If the sensor is working properly you'll see the voltage vary with your speed when you're going over about 15 mph. If it doesn't vary it's not getting a signal. You should see the voltage start at about 2v and go up the faster you go. VSS2 (in the speedometer housing) Check for DC volts in connector B46 at the TCU. This is the largest connector at the bottom of the TCU. The wire is in position 11 and is green with a black stripe. Again - I cut the wire and put the voltmeter in series. Here's the trick - now drive the car VERY SLOWLY about 4 or 5 feet. You should see the voltage go from zero to 4. You should also be able to stop the car and keep the voltage at 0 or 4. If the voltage doesn't change - no signal. Anyway - I'm about ready to give up. I might try one more transmission computer, but I'm at my wits end. I've checked everything I possibly can with no luck. I've even put back in the air suspension fuses and switch - no luck. This thing just doesn't want to work. At least I have my 4WD switch, but I'd really like it to work the way it's supposed to. Any comments are appreciated, otherwise I hope this helps somebody else doing the diagnostics. Dave

Well, still no AWD. I’ve now replaced the entire instrument panel and checked all the connections to it– no luck. It was interesting to take apart the old one though, the speed sensor is right on the speedometer and is just a little reed switch. As the speedo spins it somehow (I couldn’t see how) opens and closes the switch and breaks the connection. The computer uses this signal to do two things: set the speed for the cruise control and check against the rear axle for AWD. So it would appear that if your cruise works then you can assume your speed sensor is ok – and my cruise works just fine. In an earlier post someone said they thought there are two sensors in the combo unit – nope, there’s just one. So I guess I have just a couple more things to try before I give up completely. I need to actually check the signals going into the TCU from the speed sensors. I have the pinouts and know which wires to check – does anybody know the best way to measure the signal? The “TCU I/O Signal” pages says to check it with a voltmeter in the A/C range. If there’s a better way please let me know. Also – shouldn’t I be able to read the signals from the hookup for the select monitor? Josh – do you have the pinouts for your select monitor? That might be the best way to do it (if it’s possible). Thanks. Dave

Roadie, Thanks for the info! I was hoping somebody else had lost their AWD for no apparent reason. Unfortunately, all the lights in my dash work just fine. The only lights that don't work are on the shift indicator below the shifter. Just one question: Did you ever get a transmission error code or have the power light flash when you started the car? If not, then I need to pull my panel out and check the connections pronto. I think one of the subaru technical sites actually talks about bad shifting due to a bad connection in the dash. Is there any special trick to get it out? Thanks for the help. Dave

I've done a little more probing in the system, and I'm getting nowhere. It's going to take more work than I thought to get to the speed sensor in the tailshaft, so I haven't pulled it yet. I went to the junkyard and tried to find a speed sensor for the combination meter (speedometer), but it looks like you have to get the whole panel, I couldn't see anyway to take it apart and just get the sensor - is this correct? Also - where is the air suspension control computer? There are a couple of posts saying it's under the drivers seat, but I can't find anything under there. Do I have to pull up the carpet? How do I get it out? Thanks. Dave.

Josh, I removed the fuse for the air suspension, but did not remove the computer. I'll try that this evening. I'll also pull speed sensor 1 out of the tailshaft and take a look at it. The speedo work will have to wait until the weekend. Something to note here, my speedo has been acting up a little lately. Just makes a buzzing noise like the cable is starting to go. This only started recently but maybe its the result of something that's already gone bad. Do you have a select monitor? Where did you get it? Some days it would sure be nice to have one. Thanks. Dave.

I’m reaching my wits end with the AWD system on my ’90 legacy wagon and I’m looking for any advice I can get. It’s got an auto trans and runs great, but I can’t get the computer to active the AWD. Here’s what I’ve done: 1. Removed the extension housing from the rear of the trans and replaced the seals in the tailshaft. No observed damage or wear. 2. Put a switch in the line to the trans duty C solenoid. If I push the switch and break the connection, it locks up the rear axle and puts the car in 4WD – so I know that mechanically it’s sound. 3. Put a different trans computer in. No change – still no AWD. 4. Checked the voltage going from the TCU to the duty C solenoid per the info in Legacy777’s website. The voltage is ALWAYS at 9v+. Even when I put it in “1” and push the throttle to the floor. According to the spec sheets it should go to 0 in that condition. Also verified that there’s NO fuse in the AWD switch. 5. Checked for transmission code errors. The only errors I’ve ever found are for the duty C solenoid when I break the connection. Last night I left the voltmeter connected and took it for a drive in the snow. Got it stuck with the front wheels spinning and still no voltage change. It’s almost like there’s something telling the computer to keep it in FWD. As soon as I pushed the switch and broke the connection it dug itself right out of the snowbank, so I know it should work. The only thing I can think of is that I could have a bad speed sensor in the speedometer or extension housing, but wouldn’t it still try and lock it up with the shifter in “1” (per the shift map)? Also – if the computer senses a bad speed sensor shouldn’t it set a code? The only thing I’ve messed with electrically on the car is the height control system. I’ve removed all the stupid air struts and replaced them with regular ones. I don’t see how this could affect it, but I’m just wondering ‘cause now all those connectors are disconnected. And I don’t think the AWD was working before I replaced them. Anyway – I think I’ll head back to the junkyard tomorrow and try and find a speedo unit to mess with, and maybe exchange the computer for another one, but in the mean time I’d really appreciate any advice. Thanks. Dave

Skip – here’s what I know and what I’ve done: The TCU is located right under the dash on the driver’s side. It has three connectors in the bottom. One of the wires goes directly to the duty C solenoid and is white with a black stripe and is in the connector closest to the firewall. Here are some links to Legacy777’s website where you can see the pinouts. I think it’s connector B33 terminal number 3. I found it using my neighbors Chilton manual. http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/TCU_I-O_page1.jpg http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/TCU_I-O_page2.jpg As I understand it, the solenoid controls a valve that ports fluid to the clutch. When there’s 0 voltage to the solenoid it opens, sending fluid to the clutch and locking up the rear wheels. When there’s 12 volts to the solenoid it closes, releasing the clutch and rear wheels. As to your idea of it being a drain valve, it’s possible it could work that way, I don’t know for sure. Regardless, 12v = front wheel drive, 0v = four wheel drive. This opens up all kinds of possibilities for a switch in the line. For example, in my ’90 legacy I have replaced the height switch for the air suspension (which I removed) with a switch for the AWD. I used a defroster switch from a junkyard legacy which snapped right into place. I just spliced it into the line going from the TCU to the solenoid. When the switch is pushed in it makes a connection, putting the car in computer controlled AWD. When the switch is out, it breaks the connection putting the car in full time 4WD. And it sure goes in the snow in 4WD. Just don’t drive in on the pavement with it locked up – very hard on all the drivetrain components. You could also wire in a three position switch to do the following: Pos 1: 0v (no connection) = 4WD Pos 2: connected = computer controlled AWD Pos 3: 12v supply line = front wheel drive I guess if you’re smart enough you could use some type of variable switch to control exactly how much power is transmitted to the rear wheels (I think the WRX STI does this) but to me it doesn’t matter. I either want it AWD or 4WD depending on if I’m driving on or off road. The only downside to using the switch is that the next time you start the car you’ll set a transmission error code because it thinks the solenoid is dead. If you’re wondering why I did this to my car, it’s because the AWD doesn’t work. I found a post on legacy central where somebody else had the same problem and he fixed it this way. It’s worked great for me so far, although I’m planning on eventually fixing the problem. I think I’ve got a bad TCU or bad speed sensor – for some reason it doesn’t change the voltage when a front wheel starts to spin. Anyway – hope this helps and good luck. Dave fixed link

Skip - do a search for user "patcal" and then go to his post of "starting to hate this tranny". There are a couple of replies there about how to do the switch you're talking about. I've installed it in my legacy and it works great, push the button and it locks it up. You can also look at the legacy central board, that's where I found the original info to do mine. Dave

Ben, Please do a search for the following post: "starting to hate this car(tranny) Help!!" by Patcal. I think it's on about page 4 of the forum. He had a similar problem to yours and it turned out to be just a bad TCU. He's done some diagnostic work to determine if it was the solenoid or the TCU and it worked out pretty good. By the way - a bad clutch pack or tailshaft housing will NOT cause torque bind, it will only cause the tranny to shudder and slip when the computer locks it up in 4WD. The torque bind is caused by the solenoid opening up and porting fluid to the clutch when it's not supposed to. This can be caused by a bad solenoid, bad wiring, or bad TCU. And if you have to replace the solenoid it's very easy to do yourself if you have a little mechanical background. Dave

Sorry, I disagree with the last post. I've personally disassembled the clutch pack in the extension housing and there's no way the clutch is released by hydraulic pressure. That would mean the clutch is always squished together until you start up the car. When you take apart the clutch the discs and steels are all floating around loose. Fluid is ported to the clutch to squish all the plates together to lock it all up. My car had a bad seal in the extension housing and I replaced it when I had it all apart. From what I understand when the seal goes bad it slips and shudders when you're driving it on a slippery road, it doesn't have any effect in a tight turn.

If it binds with the fuse in I would definately check the voltage as I described above. It sounds like as it gets warm you lose the connection to the solenoid. You might want to just try and follow the wiring harness from the TCU down to the trans and check all the connections and wiring. Good luck.

Pat, Here’s some info to help you if you decide to put in a switch. The TCU is located right under the driver’s side dash. It has three connectors in the bottom. The wire you’re looking for is white with a black stripe and is in the connector closest to the firewall. Here are some links to Legacy777’s website where you can see the pinouts. I think it’s connector B33 terminal number 3. I found it using my neighbors Chilton manual. http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/TCU_I-O_page1.jpg http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/TCU_I-O_page2.jpg My idea for a switch has worked pretty good so far. When I bought my car it had the air suspension option, with a switch to change the height of the car on the right side of the steering wheel. I’ve removed the air suspension and so the switch wasn’t being used anymore. The suspension switch isn’t the right type for switching the AWD, so I went to the junkyard and bought another rear defroster switch which snaps right into the spot where the suspension switch was (I think you will have just a blank cover there). I then cut the white/black wire and ran new wires up to the new switch and put it in-line. I had to do some testing on it to see which wires actually switched, but it wasn’t too hard. So now I have two defroster switches – I put a label over the new one that says “AWD”. When it’s depressed the car is in AWD mode (solenoid connected), when it’s released the car is in 4WD mode (solenoid disconnected). I did this on my car because I can’t get the regular AWD to work, so now I can just push the button and it locks it up – and does it ever go when it’s locked up! Your case is a little different. It seems the computer isn’t putting any voltage to the solenoid, so you need to be able to switch the voltage on. When you put the fuse in under the hood it does this for you, but I’m not sure I’d drive it all the time with the fuse in. So you’ve got three options: 1. Run a 15amp fused line from the FWD switch under the hood (the little fuse box) and switch it at the dash. I’m not sure I’d recommend doing this, I don’t know what the consequences are of always running with the fuse in. I think all it does is send 12v to the solenoid all the time, but I’m not positive. 2. Run a 15amp fused ACC switched line (12v when the key is turned on) to the new switch and then to the wire going directly to the solenoid. This cuts the TCU completely out of the line, but you’d have 12v at the solenoid to keep it in front wheel drive. Again, this is a not a real good permanent solution. 3. Fix the problem – best option Quite frankly I’m surprised the fuse works. From your previous posts it sounded like you were getting solenoid errors from the computer when it was torque binding. It sounded as though you had a bad connection in the line going to the solenoid. So I’m surprised putting a fuse in fixes it. You’d think if there was a bad connection that even the fuse wouldn’t fix it (since it’s trying to send voltage down the same wire?). Maybe I don’t know exactly how the fuse works. It describes it somewhat in the links above. Here’s what I would try first: locate the wire coming from the TCU. Hook up a voltmeter to it so you can see what the computer’s sending to the solenoid and then go drive it around without the fuse, with the fuse, etc. I would also look to see if there’s voltage from the TCU to ground, and voltage to the solenoid. If there’s a bad connection you would see voltage going to ground, but not to the solenoid. Hope this helps and isn’t too confusing. Good luck. Dave

Sounds like you might have a bad connection or short in the wire harness to the solenoid. It’s a fail open version, which means that when it loses power it opens all the way up and ports fluid to the rear transfer clutch, locking it up in 4WD. The only other thing I can think of is that there may be something in the valve body where the solenoid sits that could be blocking the solenoid open. Did the mechanic clean it out good when he replaced it? I haven’t taken the solenoid out and so I don’t know what it looks like in the valve body. I’m guessing you can check the connection to the solenoid without removing the extension housing again. The trans computer is right under the dash on the driver’s side and the solenoid wire is easy to find and I think it goes directly to the solenoid. You could check and see if you’re getting voltage to the solenoid while you’re driving. From what I understand, you should have 12v when the wheels are all spinning the same speed, and the voltage should drop as one axle starts to spin faster than the other. If you have zero voltage while driving, then you probably have a bad connection to the solenoid. I’ve found the wire and put a switch in it to lock up mine in 4WD, but I can’t remember which wire it is. I can run out and check it at lunch if you want me to. Good luck, sounds like a frustrating problem but don’t give up. Dave

Yes, once you get the extension housing off the solenoid is right in the bottom of the housing. You don't have to remove the clutch pack - but if you do it's a piece of cake to take it apart and check the disks. Just make sure you put it back together in the same order. The only thing to watch out for is when you pull the extension housing off the transmission there are a couple of pieces that like to fall out. They are the parking brake locking arm and spring. Just be careful and watch where they go so you can get it back together. I have a couple of pictures of the extension housing removed where you can see the solenoid, but I don't know how to post them. You can e-mail me and I'll reply with them attached. Good luck! dashton@wencor.com

Sounds like you’ve verified that the duty C solenoid (transfer clutch solenoid) has failed. This solenoid is a fail open version, which means that when it loses power it opens all the way up and ports fluid to the rear transfer clutch, locking it up in 4WD. That’s why the fuse has no effect – normally the fuse tells the computer to put voltage to the solenoid, closing it and disconnecting the rear wheels. With a bad solenoid it will always be open regardless of the voltage applied. They’re designed this way so that if the solenoid fails you don’t lose your AWD and can get back home. I have a little experience with this – my AWD doesn’t work at all and the only way I can lock up the rear wheels is flip a switch I installed in the solenoid supply wire. When you open the switch the solenoid loses power and opens, thereby locking up the rear wheels. Just for your info – it’s a pretty easy replacement. I’ve had mine apart trying to figure out what’s wrong with it and it’s not too hard to replace. As for the trans slipping, could be several things. You should probably start with a fluid and filter change (along with the solenoid) and go from there. Good luck! Dave

The AWD on my auto trans 1990 Legacy has never worked since I purchased it two years ago. I’ve been though the whole system – removed the extension housing and checked the clutches, seals, etc. and still nothing. This summer I finally wired in a switch that cuts out the duty C solenoid to try and force it into four wheel drive. I finally had a chance to test it this weekend with the first snow and it works great! But, my AWD is still dead. Initially I thought it was because of a stuck or bad duty C solenoid, and that the switch just forced it loose, but I’m getting nothing from the “computer controlled system” even when it’s stuck in the snow – just one front wheel sits and spins. This leads me to believe that there’s something else wrong, because as soon as I hit the 4WD switch it digs itself out and goes like crazy. (very fun, by the way) Now here’s a little blurb I found on the endwrench.com: "4EAT Speed Sensors If you are in the process of diagnosing delayed or erratic shifting on a 4EAT transmission, pay close attention to the comparison of readings between speed sensor 1 and speed sensor 2 as displayed on the Select Monitor. If these sensors are working properly, the two readings should be close, but are rarely absolutely identical. If, however, in the vehicle that you are driving, you notice that the speed sensor 1 signal and the speed sensor 2 signal are always precisely identical, there may be a malfunction in the signal or circuit from one of the sensors. When the transmission computer senses a failure in one of the speed sensor circuits, it may substitute the other sensor’s reading in the display of the Select Monitor. This is why the two readings would be identical.” Could I have a bad speed sensor that is causing me to lose the AWD? It would seem to me that if the computer substitutes the signal if the sensor isn’t working then I would lose the AWD (since it’s supposed to engage when there’s a difference in the two signals). I’ve never had a trouble code for the AT (except when I put it in 4WD, because I cut out the solenoid) I would assume if the computer thinks the VSS is bad that it should set a code. Has anyone else had a problem with a speed sensor? Does anyone know how to check it other than take it to the dealer and have it scanned? Any help would be greatly appreciated. Thanks. Dave