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Discussion Starter · #1 ·
Hi,

I have a 2000 Outback Limited Sedan that has 120k miles. Fairly good condition, though parts are wearing out faster than I would like. Recently, I have had problems that seem to be electrical in nature. My Subaru dealership can't find anything wrong and recommends replacing both the TCM and the ECM (TCU/ECU) next time it happens. It was in the shop for a couple of days last week while they checked things out.

About two months ago, the AT Oil Temp light came on (solid, not blinking) while I was driving home from work. Not having seen that one before, I pulled over and turned the car off while I dug into the manual, which said "don't go up steep hills or pull things". When I turned the car back on, the light didn't come back on.

Then, two weeks ago, the AT Oil Temp light came on flashing. Restarting the car again cleared the code, but it came back within a few minutes along with the check engine light. I took it in to the shop where they couldn't find anything wrong with the AT system except for dirty fluid. They replaced the fluid, cleared the code (I forgot to ask what it was), and off I drove. Last monday the same thing happened, so I took it back in. Supposedly it was a different check engine light code (again, forgot to ask....) They spent some time checking the electrical system, and generally rooting around, but again couldn't find anything specifically wrong.

To me it seems obvious there's some electronics that are going wonky. The only suggestion the dealer has is replacing TCM / ECM for $1600 (!!!), which would be the straw the breaks the camels back -- and makes me get a 'new' used car.

The battery was replaced last year, the car is driven (for the last month) ~40 miles a day to work and back, and before that it was 14 miles daily. I have a multimeter and I'm not afraid to use it, and I have a Haynes service manual, but that doesn't have anything obvious for me. Oh, thought I'd add that I've had the head gasket leakage issue fixed about a year ago as well, as well as a right outer CV boot fix recently.

Does anyone have any thoughts as to things to check? I'm considering replacing the TCM (looks like $100 off ebay) myself since the manual indicates it's fairly straightforward and no programming is needed. Is this a good "first" step if all else fails before replacing both at the same time?

Thanks in advance!
 

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2003 OBW 2.5L 4EAT
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Get the codes read first, and post them here. It might be something other than the TCM or ECM, without knowing the codes you would be just throwing money at parts you may or may not need to solve the problem.
 

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2005 LL Bean
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If you plan to keep the car, invest in a code scanner. You can find them online for as little as $38.50 shipped. Would save you a lot of time and money not having to brought to a shop before you can at least see what the code is. Once you know what codes they pulled, you'd have a better idea of what to check. It sounds like they are taking the flat-rate approach of changing parts. What are the chances both modules failed at the same time? Even if it was one of the other, that is a lot of cash just to found out it is a sensor or short etc.
 

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Using the instructions in this thread you should be able to read the transmission codes that would have been set with the flashing AT Oil Temp light.

The CEL code is probably just a secondary warning light triggered by the TCU. The code could just be one saying that there's a TCU code or codes to look at.

In the event the problem is, for example, a vehicle speed sensor, that would trigger a CEL independently because the ECM also uses the VSS information.

Some transmission codes cannot be read by standard code readers, and this is probably the case with your 2000, which I believe uses the 2-digit transmission trouble codes; but all OBD code readers should be able to read CEL codes.

Start by trying to pull the transmission codes and see what that provides.

Like others, I doubt the problem is in the control modules.
 

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01 Outback H6 VDC, 97 GT wgn w/ ej22, 98 OBW w/ej22
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i have a 2000 lego L, auto, 85k miles, with a very similar problem.

but mine is downshifting when it should not and then up shifting again. i get the flashing AT Temp light most times when driving the car, but not always. and re-starting the engine will usually clear the flashing for a bit, but not long.

when running flat and steady at any speed, the trans will downshift for no reason, any amount of acceleration will cause it to downshift. and it usually up shifts soon there after.

if i move the shifter to 2 it will not downshift. but in 3 or 4 it will.

but here is the kicker, no CELs and the AT Temp light is NEVER flashing at start up, never. it flashes only when driving the car. the TCU never throws a code, at start up, at least the AT Temp light never indicates one at start up.

2 days before this started, i replaced an axle and as a result i had 4 CELs. but i re-seated all 3 of the wire connectors on the rear of the engine and the codes went away. i have since re-checked all 3 connectors again and it did not help.

i could only find one thread with similar issues. it was a 96 outback auto with a flashing AT Temp light while driving. but there wasn't a definitive solution posted. the owner took it to the dealer, and reported they ''found a loose ground wire''.

thanks, john
 

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01 Outback H6 VDC, 97 GT wgn w/ ej22, 98 OBW w/ej22
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I'm considering replacing the TCM (looks like $100 off ebay) myself since the manual indicates it's fairly straightforward and no programming is needed. Is this a good "first" step if all else fails before replacing both at the same time?
the ECU is just as easy to replace. if you can do one you can do the other. ebay is one source, Car-Part.com--Used Auto Parts Market is another.

good luck and let us know what you learn.
 

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....
but mine is downshifting when it should not and then up shifting again. i get the flashing AT Temp light most times when driving the car, but not always. and re-starting the engine will usually clear the flashing for a bit, but not long.

.......but here is the kicker, no CELs and the AT Temp light is NEVER flashing at start up, never. it flashes only when driving the car. the TCU never throws a code, at start up, at least the AT Temp light never indicates one at start up.

Have(had) a similar issue, but mine popped up after I maladjusted my TPS.
Still haven't checked it with VM yet but turning it forward and just using the scanner to watch values down to 4.35% has eliminated my issue.
Just a thought.

O.
 

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Discussion Starter · #8 ·
Get the codes read first, and post them here. It might be something other than the TCM or ECM, without knowing the codes you would be just throwing money at parts you may or may not need to solve the problem.
I was afraid that was going to be the first question :). I'm checking with the dealership, and will post when I hear.

Using the instructions in this thread you should be able to read the transmission codes that would have been set with the flashing AT Oil Temp light.
Thanks for those instructions. I followed the instructions and was able to get the "2 flashes / second" i.e. "All Clear" signal from the AT Oil Temp indicator.

Start by trying to pull the transmission codes and see what that provides.

Like others, I doubt the problem is in the control modules.
Good to know. I actually wonder if it might be related to the cruise control. I had been using it (I think) when the check engine light kicked in (though not always with the flashing AT Oil light...). I'm avoiding cruise control for now, so we'll see.

the ECU is just as easy to replace. if you can do one you can do the other. ebay is one source, Car-Part.com--Used Auto Parts Market is another.

good luck and let us know what you learn.
Do you have a reference on how to get below the carpet on the drivers side (I believe that is where the ECU is)? My Haynes manual doesn't seem to have that information (unless it's hidden somewhere not-obvious).

Thanks for the link - I did find a used one for $200. That would certainly save me a lot of money if I need to do it!!

Thanks again everyone for your responses. I'm trying to track down the codes, and am certainly considering getting this ODB2 reader from amazon: U380 OBDII Check Engine Auto Scanner Trouble Code Reader : Amazon.com : Automotive ... though that one wouldn't work with my newer subaru... but it's the right price...hmm, might have to wait for that.

Again, thanks all!
 

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01 Outback H6 VDC, 97 GT wgn w/ ej22, 98 OBW w/ej22
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the ECU is under the carpet on the passenger side up against the fire wall. there are a coulpe of plastic plugs/ screws / clips that go through the carpet. one in each forward corner, and then the door sill cover and the plastic trim on the door column in front of the door. peel the carpet back and then remove the protective metal cover, 3 - 4 bolts and then 3 bolts for the ECU. not a hard job.
 

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01 Outback H6 VDC, 97 GT wgn w/ ej22, 98 OBW w/ej22
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success,

i did a fair amount of research and and today the weather and my day off cooperated.

i went in to clean every wire connection on the engine as well as every ground point. i did the 3 main connectors on the rear of the engine and found no ills as well as the TPS no ills.

but as i was looking for the grounding wires on the engine i found a loose on right next to the coil on the intake. so i removed and cleaned it and then re-installed . problem gone.

woo-hoo.
 

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Onyx, 2008 LL Bean 3.0R and 2017 Honda Civic Hatchback Sport Touring
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I'm trying to track down the codes, and am certainly considering getting this ODB2 reader from amazon
Here's the one I got: OBD2 Reader Car Diagnostic Tool OBD II (MT-50) : Amazon.com : Automotive It is about the same as the one you're looking at. I use it to quickly pull and clear codes. I have some PC software (Free SSM) for more detailed analysis. You could spend 3 or 4 times as much on an Actron scanner that would certainly work with your newer Sube. But, I'm not sure why you think the cheaper one won't. The OBDII codes and plug haven't changed in decades have they?
 
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