96 Legacy Center Diff lock switch

[JSB]

Yes, I have just purchased a 96 wagon, with 182K, with only FWD, with fuse pulled, and trans serviced. I am considering the center diff lock switch to troubleshoot the problem? Also the a/t temp light flashes @ 15 times upon starting, but the trans shifts good and does not slip?? I am not a serious mechanic or electrician so keep it simple.

 

Many thanks

JSB

[WoodsWagon]

Temp light flashing means there is a code stored. The code may be retrievable with a certain input dance, there was some sequence of shifting the tranny and pushing the accelerator pedal that puts the TCU in read codes mode. Not sure if that was still available in 96 with OBDII or not, but worth a shot. Do a search for it.

 

No AWD and a code usually means a front or rear speed sensor has gone. If you had locked 4wd and a code, then the Duty C soleniod would be the likely culprit.

 

Does the spedometer still work?

[Fairtax4me]

So it's an AWD car but only the front wheels spin?

Check that the driveshaft (that goes to the rear diff) is still there. Some people will remove those completely.

 

The light is flashing because there is a fault (obviously) that the TCU (trans control module) has identified as a problem. The flashing light is a code. I don't know how to read them I've never bothered to look it up for myself, but there are plenty of threads here about how to do that. Look in the "Similar Threads" List at the bottom of the page here, or do a search for "Flashing AT Light" or something like that and something useful will pop up.

 

The code probably has something to do with the Duty C solenoid which is the line pressure solenoid for the transfer unit/center diff in the tailhousing of the transmission. Those commonly go bad and will cause the center diff to lock which locks the front and rear driveaxles together creating torque bind. Makes the car all jumpy and hard to turn when in a parking lot or going around corners similar to how a 4x4 truck would behave on pavement when put in 4 wheel drive with the hubs locked.

 

Matter of fact, you can search for "Torque Bind" here and find a ton of threads dealing with how to troubleshoot and fix this problem.

 

If the prop rear driveshaft is still in place there are a few possibilities. The clutches in the transfer unit might be completely shot. There may be a short in wiring harness going to or inside the transmission or in the control module itself.

[JSB]

speedometer works fine, driveshaft intact, transmission behaves fine just no AWD??

[idosubaru]

We need a clearer picture of what's going on. My guess is that the car has torque bind so the FWD fuse was installed (not "pulled" as you said, since there's no fuse to pull). I'm guessing since we don't know what's going on, so just clarify if something doesn't make sense.

 

Remove the FWD fuse, If the torque bind is present then you'll feel the 4WD binding in turns. Also with the FWD fuse removed:

 

1. If the trans light still blinks 16 times at start up then your Duty C has failed.

 

or

 

2. If the light doesn't blink then your clutches/hub are hosed.

 

You'll need to pull the rear extension housing to fix either of those.

 

Or you can just wire in a simple switch to control it yourself. Run it FWD, then flick the switch to lock the rear transfer clutches in 4WD. You'll have more control and better traction in really bad conditions. That's what I would do (and have done before).

[johnceggleston]

you seem to have a good understanding of the problem.

 

easier than installing the lock switch, unless you want it for later, is to unplug the wiring harness connector on the top of the trans at the rear of the engine, passenger side, at the fire wall. there should be several large connectors, i think the largest one goes to the trans.

 

this will put the trans in limp mode, driving in 3rd gear only, and it should 'lock' the wheels in 4wd. you need to know. no 4wd then you go in one direction, yes to 4wd then another. you can tell by driving tight slow circles. i've never tried it in 3rd, should be interesting.

 

also you can read the trans trouble code pretty easily. there is a black connector under the dash to the right of the steering column. ground out pin #5 and the AT Temp light will flash the code. search for a post of mine just yesterday in a thread with more info and a diagram, also with a link to an older post by porcupine73 for more info on reading the codes.

 

EDIT:

 

http://www.ultimatesubaru.org/forum/showthread.php?t=115676&highlight=668867

 

i just posted this link yesterday:

 

http://www.ultimatesubaru.org/forum/showpost.php?p=668867&postcount=5

Edited September 14, 2010 by johnceggleston

[JSB]

Will try the trans wiring harness un-plug when I get home!

 

Thanks again,

JSB

[wtdash]

How to pull codes on 4EAT (@ least 90-94): http://www.surrealmirage.com/subaru/trans.html

 

Thanks to JC/Legacy777 for the info.

[JSB]

I unplugged the trans plug and drove in tight circles no AWD, even jacked up the front end and made sure, just the front wheels turning... So what is next?

[johnceggleston]

I unplugged the trans plug and drove in tight circles no AWD, even jacked up the front end and made sure, just the front wheels turning... So what is next?

 

either you have no fluid pressure going to the transfer clutch or your transfer clutch discs are shot and not grabbing.

 

or maybe as mentioned you have a failed vss2, front speed sensor. i'm not very familiar with that and may not be a lot of help. do you have a CEL, check engine light?

[JSB]

No CEL, bought the car second hand. Is their any immediate damage in driving the car?

[johnceggleston]

No CEL, bought the car second hand. Is their any immediate damage in driving the car?

 

none, no harm until it snows and you get stuck.

 

there are 2 speed sensors, one on the front diff out put, axle, and one on the rear output, drive shaft. the computer compares the speed difference to see if more rear wheel power is needed.

 

the front vss is easy to unplug the connector. the rear one you have to remove a bolt and pull the sensor out of the hole. you might try disabling each one in turn and then both to see if it makes a difference. the ECU/ speedo uses the front one until it fails and then it will use the rear.

 

if the trans computer does not see both, it will not engage the rear wheels. if disabling the rear vss stops the speedo, then your front one is bad or disconnected. (it should throw a code tho.) if disabling the front one stops the speedo then the rear one is probably bad.

 

understand?

[idosubaru]

what he said - drive on bud, no issues.

[GeneralDisorder]

So what is next?

 

You need to pull the codes per the instructions in wtdash's post above. We can't really help you till you do that.

 

GD

[rainman19154]

U bought the car second hand? Are u certain there is a working bulb in the CEL socket? When u first turn the key ON before starting, does your CEL light up with the other dash lights?

 

You should see it lit with the key ON but the engine not started. It should go off after the engine starts. If you don't see one before cranking it over, the bulb is bad or has been removed.

Removing the bulb is a ploy used to hide problems with used cars. "No CEL. Hmmm that means no problems."

[GeneralDisorder]

The "AT temp" lamp flashes indicating stored codes for the TCU, not the CEL. And it only does it on some models if you turn the ign. on/off/on in rapid succession. The CEL will not indicate faults with the TCU - they are not hooked together.

 

GD

[JSB]

will try to figure out the TCU codes this weekend,

Thanks for all the replies!