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98 Impreza Outback Sport - AWD Cutting Out
Posted 08 January 2005 - 08:36 AM
Dash FWD light is not on.
Can a fluid change help?
Posted 08 January 2005 - 11:38 AM
A power flush of the tranny fluid may help.
The AWD system on your automatic is controlled by the Tranny ECU (TECU)
watching the two Vehicle Speed Sensors (VSS).
Simply put, one VSS watches the front wheels the other the rear.
When a programed differential for a certain time exists the TECU sends a signal to the Duty Solenoid C (DS C) located in the tailshaft of the transaxle.
This solenoid controls hydraulic fluid flow to a clutch pack that engages the rear driveshaft.
A noteworthy point here, DS C controls the drain for the clutch pack.
If DS C goes bad or is disconnected the rear shaft is connected similar to a 4wd system as all the fluid pressure goes to lock up the rear drive.
Question for you: does the "power" light flash when the car is started?
If so there will be an error code stored in the TECU warning of
which component is not functioning
Legacy777's website has an excellent write up on how to retrive and read these codes.
Might want to start with a power flush or just a drain and fill.
Posted 08 January 2005 - 11:52 AM
Disconnected the battery just now to clear the codes. Will see if that helps.
Power light? Unclear what that is. All light come on, ABS on then off. Starts, all lights off (except for airbag light - I know...I have to get that fixed - $400 for the part).
Thanks for the help. Great site.
Posted 08 January 2005 - 12:06 PM
You car does not have the "power" light
you may need to get the codes by using a scan tool.
Posted 08 January 2005 - 02:22 PM
the 4WD not engaging is unlikely to be rear diff related. if it's never been flushed, now would be a great time to flush your ATF but i wouldn't be surprised either way....if it fixed the problem or not.
if you drive through snow or off road much i'd consider splicing a switch in place to manually lock your 4WD. (the technical terminology would be that you're splicing a switch in line with duty solenoid C, thereby locking your rear trasnfer clutch). then you control when lock-up occurs. then install a visible light which is connected to the same 2 pole switch so you know when it's on or off. don't want to leave it on when driving on pavement or lots of turning. this switch is nice, leaves the 4WD drive *locked* instead of the TCU cycling the DS C on and off as it detects slip. and if you're having a problem locking up, this might be a good work around and give you more capabilities. it's very easy, just a matter of splicing one wire, the one to Duty Solenoid C. unfortunately i don't have lots of OBS information so i can't tell you which wire. though i will find out soon because i am picking up a *new* 1997 OBS in a matter of minutes.
i attached an under hood picture showing only the one wire you'd have to splice in a 4EAT. run this wire to the center console and simply install a switch to engage/disengage Duty Solenoid C....and even when it's *Off* or out of 4WD, it will act as normal and engage/disengage as necessary like it normally would.
Posted 08 January 2005 - 03:00 PM
Funny tho. It will stay engaged for 1/2 mile or so in the snow, then stop locking up. FWD only then. After it stops AWD forward, reverse will not work either. Stop and run an errand, come out and it will be AWD backing up and AWD for a short distance.
This switch grounds the wire to the DS C solenoid? Runs power there?
What could explain this intermittent behavior? I'm thinking if it works for a short time, then it's not mechanical. I'm crawling under later today to see if it's mechanical, like a wire, etc.
Posted 08 January 2005 - 03:05 PM
Posted 08 January 2005 - 03:06 PM
follow all the wires you can, like the rear speed sensor wire should be near the back of the transmission by the extension housing. the actual Duty Solenoid wire may be internal more than external so i don't know that you'll get a good look at it.
this is in the snow right? if this was on dry pavement i'd wonder if something is wrong with your tires. do they match? are they properly inflated? are they wearing evenly? a mismatch will cause problems with the transfer clutch locking.
Posted 08 January 2005 - 04:51 PM
Here's a tidbit. One I step on the brakes with the light offs, the dash lights illuminate along with the standard "click" of the transmission unlock. This smacks of a grouding/wire problem.
Posted 08 January 2005 - 05:00 PM
Posted 08 January 2005 - 10:43 PM
Seemed like from the info here that ABS is a separate beast from AWD system.
Posted 09 January 2005 - 03:23 AM
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