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No AWD – help!


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36 replies to this topic

#1 dashton

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Posted 08 January 2004 - 09:24 AM

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

#2 Legacy777

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Posted 08 January 2004 - 09:36 AM

Dave,

wish you were closer and I could plug in the select monitor. There are two speed sensors. Speed sensor 2 is in the combination unit on the dash and displays the speed.

Speed sensor 1 is in the tail shaft, and that would be the one that could be causing you issues. It "should" leave a code if it's not working though.

When you took the air susp out......did you remove the fuse for the air susp, did you rip out the computer and associated parts?

#3 Skip

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Posted 08 January 2004 - 09:54 AM

Dave, I agree with Josh. It sounds like one of VSSs is not outputing the correct signal. The TCU is just looking for continuity I believe so if it is connected but not sending the correct signal it will not show a trouble code.
Your idea of a new speedo head may prove beneficial.
Maybe someone (Josh?) knows what the signal from the VSS looks like and with the aid of a 0-scope you could watch and verify their outputs.


#4 ScoobySchmitty

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Posted 08 January 2004 - 12:06 PM

I know there is supposed to be a fuse plug somewhere in the engine compartment that will allow you to have the car drive in FWD, instead of AWD. I can't remember if I saw this in my Haynes manual, or if it is in the Subaru manual. Look around in your engine compartment, and see if you see a fuse plug, probably near the firewall. I have a 5 speed, so it's AWD for good, but I do know of this little FWD fuse. I believe it was primarily to allow the car to be towed without damaging the AWD transmission. I hope I'm just repeating back old news, but if not, I hope this post helps out. I'll find out where exactly that fuse is and post it. Cheers, and good luck.

#5 dashton

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Posted 08 January 2004 - 12:08 PM

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.

#6 1 Lucky Texan

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Posted 08 January 2004 - 01:40 PM

Not trying to thread-jack but - what is a select monitor?

#7 Legacy777

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Posted 08 January 2004 - 02:54 PM

Not exactly sure what the output should be...probably some oscillating or on/off signal

This page has some info....
http://www.main.expe...U_I-O_page2.jpg

The speedo base can get cranky as well as the cable can make some noise.....shouldn't really affect/cause the problems you are having though, because it's for the main speedo meter
http://www.main.expe...docablebase.jpg

Yeah I have a select monitor. I got it off of ebay. I lucked out, found one with the cartridge for my car. You gotta have the select monitor and the right cartridge. It's pretty cool. I can see all the sensor values, and what's going on. The OBD2 computers are more sophisticated and tell more details....but you can use alternative methods besides a select monitor to read them.

lucky texan, select monitor is subaru's scan tool they use to read the computers.

#8 1 Lucky Texan

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Posted 08 January 2004 - 11:26 PM

OK, is it like say an Innova scanner? Is select a brand name? Is it more sophisticated than a scanner?

#9 DAlgie

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Posted 09 January 2004 - 01:30 AM

My '93 Legacy has a VSS#1 fault, the tailshaft one, and it has AWD working well. The problem I have is the auto won't upshift on it's first shift up from start. I think the ECU tries to find the VSS and after a bit decides that it's not there and goes for a base trans map instead of a closed lop map.

#10 Legacy777

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Posted 09 January 2004 - 09:13 AM

Not sure what an Innova scanner is. Select monitor is made by some company for subaru. it's the only "official" diagnostic computer for subarus.

#11 dashton

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Posted 10 January 2004 - 12:39 AM

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.

#12 roadie

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Posted 10 January 2004 - 09:51 AM

Dave, I also have a '90 legacy w/4eat where the awd did not work (drove me up a wall). When I bought the car I did not know it didn't work until after the first snow I drove it in. One afternoon shortly after that snow storm I noticed a square green lighted box around the "D" on the instrument panel come on (did not know that these lights even existed). Also found out the little car meter at the top of the instrument panel worked. About an hour later they went out. Over the course of the next few months they would come on for a short while and then go back out. I thought nothing of it until they came on in a snow storm one afternoon. To my surprise the car kicked butt. I put my wife behind the steering wheel and got out to check the situation. Sure enough the back wheel spun as well as the the front. When the lights went out I got out and checked again and nothing happened at the back wheel (the epiphany).
I took the car to my local Subie dealer and told them the problem. They told me "yes the lights don't work" and "yes your awd does not work but we will have to diagnose it further because after a couple of hours of looking we can' t seem to locate your problem". So I unhappily paid my bill and drove my non working awd legacy back to square one.
I messed with a bunch of possibilities but resigned myself to the fact that I had a fwd that was supposed to be an awd.
A little while back I read your post about running a switch from the tcu. I liked the idea (what the hell nothing else worked). I went into the garage to check things out and decided to rip the instrument panel out just to see if maybe there was a problem with the connection to the the meter and gear indicator lights. When I grabbed the connectors the lights came on. There seemed to be a bad connection between the the panel and the connectors. I wiped everything off, applied a little dielectric grease, put a cable tie around the wires and put it back together. So far so good.
If I remember correctly I think you said your indicator lights didn't work. If thats the case this could be a possibility.
I hope this will help.

#13 dashton

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Posted 11 January 2004 - 08:21 PM

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

#14 roadie

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Posted 11 January 2004 - 10:26 PM

Dave,
I never had a transmission error code that I can think of. As far as the power light blinking: they (power & manual lights) happened to be part of the connector that had the problem so they also did not work. Strange thing is that the dealer said the power/manual switch worked even though the lights didn't. The lights now work fine since fixing the connector.
To remove the instrument panel first remove the bezel around the panel. You have to pop out the air vent to the left of the steering wheel and center of dash (pry out with knife or sharp instrument). Next pop out the power mirror switch (the whole unit as one) and rear defrost/cruise switches (again as one unit). Pop out switch or blank panel to right of steering wheel (I'm not sure if you have something there but mine is blank). Next pull drink holder all the way out. Comes out like an ashtray. Behind all those items you pulled out are screws holding the bezel. There are also two screws above instruments and two above climate controls. All told there should be eleven screws.
Now you have to fish bezel out and over steering wheel. Have fun. When you get it partially out, disconnect the hazard switch.
Once that is out of the way, there will be four screws holding on the instrument panel. remove those and the panel will be loose. The only thing keeping you from gaining access to the back of the panel is the speedo cable. Slide that off and it should pull out far enough to see the back of it.
If it means anything, the connectors I had problems with are top center.
I hope you find your problem. I know how you feel. I've owned this car for four years and I rectified this problem just a month ago. It seemed to bother me more in the winter than during the fair weather months.
Good luck.

#15 dashton

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Posted 14 January 2004 - 01:04 PM

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

#16 Legacy777

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Posted 14 January 2004 - 03:55 PM

The reason the tcu i/o page says to use the ac function on the meter is because it should be an oscilatory signal.

You really can't just hook up to the select monitor pins. The ECU/TCU sends information about various sensors in a propriatary select monitor protocol. The select monitor and specific cartridge must be used to decode the incoming information so it can be displayed as useful information.......sorry.

#17 frag

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Posted 14 January 2004 - 07:13 PM

777, with Harrison's OBDScan tool you get the codes but also real time readings of the sensors ouput. What more info does the Select monitor give?

#18 nathan

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Posted 14 January 2004 - 07:50 PM

My 2cents. The air system is tied to the speed sensor(drops over a certain speed). I don't know but there may be some way that you disabled something when you took out the air system that is connected to that speed sensor. I took out the air system in my legacy but only removed the shocks, switch, compressor assembly and solenoids, no computer stuff or other electrical connections. Try double checking.
Did the AWD work before you did the swap, if so it is most likely the cause of the problem, if not then good luck.

#19 Legacy777

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Posted 14 January 2004 - 08:58 PM

frag,

for obd2....you probably won't have any difference or too many differences. I don't really know......only dealt with the select monitor for OBD1.

#20 dashton

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Posted 15 January 2004 - 11:48 PM

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

#21 meep

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Posted 16 January 2004 - 02:23 PM

1. do you have ABS?

2. Does the TCU interface with the ECU?

3. Personally, I REALLY LIKE your manual switch solution.

Mike

#22 dashton

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Posted 17 January 2004 - 09:11 AM

1. Yes, the car has ABS and it seems to work just fine.

2. I think the TCU does interface with the ECU. At least it would make sense that it did. I think that's how it knows when to shift - by the throttle position, etc.

3. I like my manual switch too, but would like the regular AWD as well.

I'm going to check one more thing this morning. I'm wondering if I'm possibly getting some voltage in the line from the FWD switch. There's no fuse in, but I wonder if there could be a short somewhere that could be holding it in FWD, but not lighting up the indicator in the dash. Dave

#23 patcal

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Posted 17 January 2004 - 12:35 PM

Dave,

After all the help you gave me I wish I could help. I do have a TCU you could try if you can't find one there.

#24 meep

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Posted 17 January 2004 - 01:58 PM

I don't think its the TCU. Wondering if it's getting erroneous data from ECU.... ie., in gear 1, pedal floored it should kick in, right, well...what if it doesn't know it's floored. Also wondering if speed sense might be contributed by ABS-- that's what I thought they did, at least on other cars.

[scratching head]

mike

Is there a seperate power feed to the TCU to drive the solenoid? Wonder if wiring in front the TCU is weak.

#25 dashton

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Posted 19 January 2004 - 11:43 PM

Mike,

Just finished checking ALL the inputs to the TCU that I think could affect the it - everything checks out perfectly in range. The TCU has a couple of inputs that see the throttle position and all of them check out. I also verified that the AWD switch is working properly, which it is.

One last question before I give up: Is the 2WD TCU different from the AWD TCU? I think I've heard they're the same, but I just want to be sure. Just wondering if some idiot before me replaced the TCU with the wrong one. I've replaced it again from a wrecking yard car, but I found one with exactly the same part number and letters. Maybe I need to try one more TCU - I think he's got another he'll swap me for that's a little different. Anyway, thanks for all the help. Dave




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