I have a 98 forester and also a 2001 forester parts car. The 98 set trans code 24 and had torque bind, so I put in the FWD fuse, which mostly works, however sometimes at startup the temp light starts flashing and torque bind occurs even with the fuse in. I thought this means the duty c solenoid is bad, but more reading tells me it could be the TCU failing, so (Finally) my question is, will the 2001 TCU work perfectly, or even just for testing?

No, the 01 tcu won't work in your 98. You need one from a phase 1 car. Direct replacement will be from a 96-98 outback. But any 95-98 can be used for diagnostic purposes.

What he said.  They very rarely fail so demand is so low they should be cheap if you can find one.  I think yards just price them high in the hopes that someone local needs one ASAP and otherwise 99% of them get scrapped.  When I was parting out cars I never sold one..or maybe one I've forgotten about.  someone on here probably has one - post in the parts wanted forum or look at www.car-part.com

 

The TCU's rarely fail but that is a cheap and easy diagnosis.  

I've got a couple of 4.11 final drive phase 1 tcus from the first few cars legacys I parted out. They've been sitting on a shelf for about 8 years now.

 

Duty C solenoid failure is much more common than tcu failure. There have been a few cases documented on here over the years. But it is very, very rare.

They've been sitting on a shelf for about 8 years now.

haha, that's about how those go, you've got a better memory than me.  maybe 1 of mine met the "keep at least one" criteria during a clean out scrap phase but i have no idea. 

Check the connections on the TCU first - the Forester is Impreza based and those usually won't interchange with Legacy's. Two plug vs. three plug IIRC. 

 

GD

Check the connections on the TCU first - the Forester is Impreza based and those usually won't interchange with Legacy's. Two plug vs. three plug IIRC.

 

GD

That's a phase 1 vs phase 2 difference. Not legacy vs impreza difference.

 

Case and point.

https://m.ebay.com/itm/98-1998-Subaru-Forester-TRANSMISSION-COMPUTER-MODULE-UNIT-TCM-TCU-31711AD660-/122675307739

GD, I read that the '00+ TCUs have a more gradual AWD engagement than the '99s.  Our forester has issues with RWD not kicking in when the fronts slip until you remove some engine load.  Would the later TCU help this, or would that be Duty-C failing?

I spoke to SuberDave about the 4EATs and he sad if they're going bad, there isn't much you can do to repair them.  Best bet, he suggested, was to find a smooth-shifting AT to swap in instead of repair.

 

Thoughts?

That's a phase 1 vs phase 2 difference. Not legacy vs impreza difference.

 

Case and point.

https://m.ebay.com/itm/98-1998-Subaru-Forester-TRANSMISSION-COMPUTER-MODULE-UNIT-TCM-TCU-31711AD660-/122675307739

 

No - some of the phase I Impreza models used a TCU with only two connectors. While the rest of the Phase I's used a three connector TCU. Look it up - you'll see. Lookup a 95 Impreza TCU. 

 

GD

GD, I read that the '00+ TCUs have a more gradual AWD engagement than the '99s.  Our forester has issues with RWD not kicking in when the fronts slip until you remove some engine load.  Would the later TCU help this, or would that be Duty-C failing?

 

I spoke to SuberDave about the 4EATs and he sad if they're going bad, there isn't much you can do to repair them.  Best bet, he suggested, was to find a smooth-shifting AT to swap in instead of repair.

 

Thoughts?

 

I would tend to think this is not correct behavior so I doubt changing the TCU would help much. The Duty-C itself may not be the problem - could be the transfer clutch pack is slipping at low Duty-C frequency. There is a port on the transmission you can use to check transfer clutch line pressure and correlate that to duty cycle. If you see low line pressure it could be an indication of a leak, or a poor transfer clutch piston seal, or just low line pressure which would generally be a replace transmission situation unless you want to do a complete tear down on it. I've done TH-350's, 400's, and 700R's, etc but the insides of the Subaru automatic (past the gates of the transfer clutch) are a bit of a no-mans-land where few enter, and virtually no one returns.....

 

GD

Edited March 2, 20188 yr by GeneralDisorder