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4EAT, TCU bad?


jes.

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I have a 2nd gen Legacy GT, ~195k miles, w/4EAT... little or no rear drive.

 

I thought it might be a problem with the clutch packs at the rear of the trans, but I'm thinking it might be a TCU problem.

 

symptoms:

  • no DTCs
  • no warning lights
  • FWD jumper doesn't affect behavior
  • all 4 tires off the ground, ran through all gear positions...
    • rears tire spin a little, not the same behavior as front
    • FWD jumper doesn't affect behavior above
    • ABS light now on

    [*] disconnected TCU, got expected DTC...

    • torque bind
    • car will idle forward straight, but comes to stop when turning wheel w/o throttle.
    • locked in 3rd?

 

I'm heading to the local pick n pull to search for a TCU...

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Probably the Duty C solenoid is dead, esp. if the FWD does nothing. it can be replaced w/out dropping the trans, but it's still a PITA.

 

You'd also want to rehab the transfer clutches while in there...search and you'll see what all is involved.

 

If the TCU fixes it then you're lucky!

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There are some transistors that can burn out on the TCU. If you crack open the case it should be pretty apparent if that has happened as they will look kinda melted.

 

Yeah replacing the duty c sucks. I've done it. In my case it didn't really fix the problem. I did a ton of diagnostics and still haven't gotten to the bottom of it.

 

At least the TCU is super easy to access and get at. You just need to make sure you get the right TCU to match your vehicle.

 

Could be the duty C, worn clutch packs, or grooves in the clutch drum assembly, bad wiring, TCU, or any combination thereof.

 

Links to FSM diagnostic procedure for a first gen:

http://www.main.experiencetherave.co...id_c_diag1.jpg

http://www.main.experiencetherave.co...id_c_diag2.jpg

 

A second gen probably has different wiring but the above should help you search for the FSM procedure for your model and will give you some more ideas as to diagnose the issue.

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Plugged TCU back in, cleared DTC. ABS light went out immediately after the car started moving... local yards don't have matching #s, waiting for online order to arrive...

 

 

Sent from my iPhone using Tapatalk

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  • 3 weeks later...

Swapped TCU for test... no change. Swapped back.

 

No transmissions available through Subaru...

 

Options, fix clutch packs for rear drive on a ~195K mile 4EAT or replace with complete rebuilt 4EAT & T-convertor...

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