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Old 09-15-2019, 04:40 PM   #1
Scooby Newbie
Member#: 506367
Join Date: Sep 2019
Location: Atlanta Ga
2001 OB-LL Bean

Default AT OIL TEMP LIGHT Flashing 2001 OB (Bean)

My daughter purchased used Bean OB (2001 Outback/L.L. Bean; 3.0 Engine, 4EAT transmission) in April, 2019 with ~147K miles. AT Oil Temp light issues (see below) started @ ~154,500. I’m am fairly experienced with working on cars, but this is my first Subaru. Experience with transmissions is limited to basic maintenance/service.

Overall the OB looks to be in pretty good shape – engine runs great, ride is solid, etc. I’m now debating whether to try and fix the OB or just cut my losses. I have extensively researched the ”AT Oil Temp light flashing” issue online, and would GREATLY appreciate any advice offered on what my best options are…fix the OB or get rid of it and cut my losses?

And for all you fathers with daughters out there, this is a classic “rescue daddy” situation. I would much prefer to fix the OB if possible as this is my daughter’s first experience buying a car on her own. I’d like for it to not be seen as a tragedy by her (just maybe with a lesson learned that asking dear ol’ Dad for help early is a good thing).

Current Symptoms
  • AT Oil Temp light flashing Code 79 (Transfer duty solenoid) with OB going into AWD mode (torque bind, etc.) as soon as AT Oil Temp light starts flashing.
  • AT Oil Temp light flashes and goes into AWD mode whether in normal or 2WD drive mode (fuse inserted)
  • BUT…the OB will go much longer/farther in 2wd mode (fuse in) before symptoms arise than in normal mode (fuse out)
  • Definitely temperature related more than miles driven - AT Oil Temp light never flashes in cool weather or when driving through rain.
  • And AT Oil Temp light stops flashing once car is cooled down, only to arise again after being driven in hot weather, stop & go, etc..
  • Also…Check engine light recently came on with code indicating misfire on cylinders 2 & 4. I believe this in unrelated but wanted to mention just in case. Probably just needs new plugs?

Maintenance performed (so far)
  • Completed 3 drain/refills on trans fluid, with new trans filter installed on 3rd drain/refill. This seemed to offer some improvement in that OB now goes further/longer before AT Oil Temp light flashes and AWD mode kicks in.
  • 1st drain refill indicated that trans fluid had likely never been changed/serviced. VERY dark brown (nasty stuff).
  • Also completed 2 drain/refills on rear differential and 1 drain/refill on front differential. No noticeable improvement noted. Condition of drained differential fluid reasonable, with no noticeable contaminants or metal shavings present (I’ve seen much worse).

I went to a highly recommended local independent Subaru shop and was told that if AT Oil Temp light flashes and AWD symptoms arise in 2WD, problems are deep within transmission and the only fix is to replace transmission at minimum of ~$2,500. I was about ready to write the OB off at that point, but after looking into issue a bit further online, I question whether this is truly my only remaining option. Based on what I have been able to find, it looks like a DIY project to replace the transfer duty solenoid & clutch plates will very likely resolve the issue and get the OB back on the road again.

Is there anything else I missed that I should consider as possible solution/fix?

If not, is it worth the effort to try replacing the transfer duty solenoid myself (along with clutch plates)? I’ve looked online, and I believe this is something well within my capability. But it is a helluva project, and I don’t want to do it unless there is at least a reasonable chance of success. The best link I found for transfer duty solenoid replacement is at https://forums.nasioc.com/forums/sho....php?t=2501432. Any advice, suggestions, references, links, etc. are much appreciated.

Finally, before considering replacing the transfer duty solenoid myself, I thought I’d do one more drain/refill of trans fluid and add BG ATC additive to see if this helps. Sound reasonable?

The over-riding question to all you Subaru enthisiasts out there is, “What would you do if you were me?”

Thank you so much in advance for any assistance offered. This is my frst post on your forum...hope it is OK.
Burtman is offline   Reply With Quote
Old 09-20-2019, 05:28 PM   #2
Scooby Newbie
Member#: 506367
Join Date: Sep 2019
Location: Atlanta Ga
2001 OB-LL Bean


After carefully studying the FSM A/T Control System schematic & digging a bit deeper into the harness setup, I walked through the troubleshooting diagnostics in the FSM and got the following:

Step1 – Check transfer duty solenoid
  • PASSED @ 12.6 ohms; within req’d 10-17 ohm
  • Also checked at B54 conn @ TCM (#15 - #16/ground) and got almost exactly the same resistance
Step 2 – Check harness between TCM & Transmission
  • PASSED @ 0.2 ohms; less than required 1 ohm
Step 3 – Check harness conn between TCM & transmission
  • Passed @ OL; greater than req’d 1 Mega-ohm
Step 4,5 – Check TCM output signal in “P”
  • PASSED @ 0.139V; less than req’d 1V
  • Note: For steps 4,5,6 - I measured voltage from back side of B54 connector @ #15 while plugged into TCM.
Step 6 - Check TCM output signal in “D”
  • FAILED @ 4.05V; less than req’d 5V to 7V range
Per FSM, indicates "poor contact” in xfer duty solenoid circuit OR replace TCM
I'm not sure how to test for poor contact in xfer duty solenoid short of taking it out (and replacing). And if this doesn't fix it, I assume replacing the TCM is my next step?

I still have to check resistance through transfer duty solenoid when engine is hot and AT temp light is flashing (AWD is triggered). I plan to do this tomorrow. I'll post what I find.

I sure would appreciate a litte advice and guidance from you Subaru experts...all I am getting is crickets.
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Old 09-20-2019, 09:43 PM   #3
Scooby Newbie
Member#: 506367
Join Date: Sep 2019
Location: Atlanta Ga
2001 OB-LL Bean


Just got through test drive. FWD fuse out. AT Oil Temp Light came on. Pulled over to take readings...
  • Checked at B54 conn @ TCM (#15 -ground); R = 17-20 ohms
  • Checked at B54 conn @ TCM (#15 - #16); R = 20-24 ohms
Seems to me that the above should be much closer to the same values? And both should be within 10 -17 ohm range per FSM.
Left engine running, checked voltage @ B54, #15 to ground
  • 12.68 V in "P" (should be < 1V)
  • 12.68 V in "D" (should be between 5 and 7 V)
Any ideas? Do readings make any sense at all? Do I need to check again?

BTW...I have checked to the best of my ability and I do NOT have VDC.

Burtman is offline   Reply With Quote
Old 09-21-2019, 04:04 PM   #4
Scooby Newbie
Member#: 506367
Join Date: Sep 2019
Location: Atlanta Ga
2001 OB-LL Bean


OK...I keep posting my progress in hopes that someone might help at some point. I have checked and double-checked readings:

When engine is hot and AT Oil Temp Light flashes:
  • Transfer duty solenoid resistance is between 20+ to 24 ohms.
  • NOTE: Resistance readings tends to drop rather fast – I had initial reading in high 20’s up to 30+ (depending on how fast I could get to location with meter). I assume this is due to temperature?
  • TCM output voltage in “P” & “D”” is 11.83V (FAIL per FSM)

When engine is hot and AT Oil Temp Light NOT flashing:
  • Transfer duty solenoid resistance is 33 ohms (steady)
  • TCM output voltage in “P” is 0.16V (PASS)
  • TCM output voltage in “D”” is 4.49V, which is very close to the 4.05V initial reading I got with engine cold (FAIL req’d > 5 V min)
I attached a PDF of a table I created of the readings…hope it comes through and is helpful.

  • Torque bind occurs ONLY when AT Oil Temp Light Flashing
  • Definitely temperature related – symptoms disappear as soon as engine allowed to cool down for as little as ~30 minutes. But come back quickly unless engine allowed to cool completely
  • Shifting between gears seems a bit “hard” (with no light flashing / torque bind). This may normal for a Subaru (seems like I read that somewhere) but though it worth mentioning.
  • OB does NOT have VDC

I thought it interesting that whenever AT OIL TEMP light flashin, there is a direct correlation to high output V readings @ TCM. Maybe the solenoid is going open circuit internally when hot (burned out) and needs replacing?
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Old 08-19-2020, 10:54 PM   #5
Scooby Newbie
Member#: 517838
Join Date: Aug 2020

I feel your pain.... code 79, flashing light, torque bind all the same symptoms. except sometimes mine starts flashing as soon as its started... completely undriveable because im afraid of messing it up real bad... already replaced the trans with a 50k unit and still have same issues. i took the old trans apart today to have a look at thr transfer duty solenoid and clutches and they all look excellent.... ive got a used TCM on the way from ebay, i hope thats the problem..... EDIT: 99 forester L, 2.5.... EDIT, EDIT: I JUST NOTICED THIS WAS AN OLD THREAD... HAHAHA
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