Are TCMs interchangeable? 06 LGT 5EAT

[3rd4thGen]

Car is an 06 LGT 5EAT

Like the title says, are TCMs interchangeable? Like can I use a used one from a 07 or 05 cuz I cannot find one anywhere for my yea. I’m throwing a p0600. 0700 & 1718 with er hc & Flashing cruise. Car shifts very erratically but less so in sport mode with manual shifting. When in drive it will shift up into 5th gear when I’m at 1/2 throttle or more before I even hit 35 mph and other times will go to redline before shifting at same throttle position. Basically shifting is inconsistent as hell. Either too soon or too late. Totally erratic. Sometimes the car just lags 1st gear too. If I can find a used one to try that it would be great but there are NONE for my year. Would another year work? They are different part numbers for each year so I wouldn’t think so. New they run like 600 IF I can even find one since Subaru discontinued the part. Plus programming will run like 2-400. I won’t have that much money til January when it won’t matter since I’ll be dropping like 20,000 into the car. But until then I have to get to school which is about to start and I’m worried the car will crap out on me. It just shifts so bad. AAMCO said the fluid is fine in it, too. 
 

Any other opinions on what it may be would be great!? But will I be able to use a used TCM from an 05 or 07? Since they are way cheaper and also won’t need to be programmed? If i should try something else to fix it let me know as well! 
 

Please help!! Thank you!

[GearJamr]

I don't know if they are interchangeable but have you looked on car-part.com, or a local pick-n-pull to get one?  Hell, checking out some jdm shops might get you one.

Not sure if this is the part # you are after but a place like this might help:

Used 2006 Subaru Legacy Tcu Tcm Transmission Control Module Oem 2.5l P/n 31711ak100 for Sale | 31711AK100 (partrequest.com)

Edited October 7, 2022 by GearJamr

[3rd4thGen]

Wrong part number. That’s the N/A. I drive a GT. Thank you though! I’m going to start calling all the pick a parts around to see if I can find one. Phoenix is a huge city so hopefully I’ll get lucky. If anybody has access to a totaled 06 GT automatic that can pull one I’d appreciate it! I’ll try to locate one local. Legacy gts are really really rare in Phoenix though. Like once a year if that I see another one on the road. Not like the mountain city’s where every other cars a Subaru 

[3rd4thGen]

I found one on that website though!!! Thank you so much!!!!

[m sprank]

Technically no.  There were at least 9 different part numbers for the AT control unit from 05-09.  Best advice is to note your vin and contact a dealer requesting the current part number for your vin.  From there you can make an informed decision on what works for your car. 

[3rd4thGen]

Yeah, for the 06 GT 5EAT it is 31711AK390. I didn’t figure they’d be interchangeable bc every year and N/A vs Turbo are all different part #s. I was able to find the right one luckily. Just doing a Google search wasn’t coming up with anything but the link above got me to one. I didn’t figure they’d be interchangeable. Hopefully that’s my problem. The shifting is so erratic, it seems that it’s a good place to start with those codes. Other people were saying change the fluid may fix it but AAMCO said there was nothing wrong with it. So we’ll see. It will be here in a few days. If anybody has any other ideas on what could be causing that, please lmk.
 

I also have a p0021. A previous owner had already removed the banjo bolt screen on the driver side. It wasn’t jammed in the OCV as I removed that to check. I’m guessing I just need to change the OCV out.

[m sprank]

Check oil pressure and test the ocv.  It's just a 12v magnetic coil. Apply power and ground and they open. Remove and they spring closed.  Polarity does not matter. 

[3rd4thGen]

Thank you! I was wondering if polarity mattered when testing the valve.

 

So, I changed out the TCM today. Took a whole 5 minutes. I drove the car and no more erratic shifting. Shifts great, no more slipping. Nothing at all. The first test drive after swapping it still said er hc. Then I turned the car off and back on and it went away. Maybe it was still stored in the ECU or something and needed the extra off/on. I  need to get the codes checked and I’m hoping just 0021 is the only one remaining. OCV will be here on Tuesday. Freakin 8 days to get here from the time shipped. That’s ridiculous. UPS surepost is CRAP and can suck it! I live in Phoenix. Usually 2-3 days to get here from anywhere in the US. I’ll look up the procedure for checking codes from my car later or I’ll just go to autozone. I’m almost positive changing the TCM cleared a few codes though. Night and day difference, so I’m sure my TCM was bad. It downshifts when I give it gas now, up shifts properly. Needle doesn’t looking like it’s slipping. Definitely made a HUGE difference. 

[m sprank]

Normally you want to reset the learning on the TCM.  That takes a VERY expensive scanner or a trip to the dealership.  Autozone wont be able to reset tranny codes, but they might be able to read them.  ECU codes should not be an issue.  I posted instructions long ago on how to use the dash to read TCU codes on 05-07 5EAT's.

 

UPS Surepost is a joke.  UPS takes a package and delivers it to the post office who then delivers it to the addressee.  The hand off to the USPS is the killer.  It is an inexpensive way to ship, but the service is horrendous.  I live in BFE, if it ships Surepost, I dont buy. 

 

Good luck with your continued troubleshooting. 

Edited October 15, 2022 by m sprank

[whitexc]

Can't you download FreeSSM and clear memory on the TCU via a VagCom cable?

I reset mine now and again and go through a very simple relearn process(drive it normally...) due to what I believe to be a failing Turbine Speed Sensor 2 that I don't want to change. Car drives fine for a while and begins to get a lazy 2-3 slide/bang shift. Reset sets her straight and takes less than a minute. 

[m sprank]

I have no experience with freessm or any other app. Ecuflash, romraider, multiple versions of Cobb software, EcuTek, AEM Infinity, etc. Have not used a vag com cable since maybe 2009?  They did not work with all model years and were rather glitchy.

[whitexc]

https://freessm.software.informer.com/

I downloaded it onto my laptop. I've never used it for anything other than the TCU reset but you can monitor and make small changes to ECM and TCM with the knowledge to do so and it's free. You must have the correct cable for USB/OBD linking and they can be had fairly cheap on your favorite web shopping hub. 

I found it researching the bad 2-3 shift I was getting shortly after buying my 2009 with 53k on it a few years back. The dealer wanted nothing to do with resetting the TCU, not without a 1 hour diagnostic fee and of course giving you a quote to replace the valve body for over $3k. That is when we as enthusiasts get crafty lol. 

It may not work for other years but I am stoked I found the workaround until I get to swapping the $40 sensor. 

Edited October 16, 2022 by whitexc

[3rd4thGen]

So to turn off the CEL I have to reset the TCU? It’s. It’s not something that just fixing will turn off on it’s own? I know some parts just fixing the problem will turn the light off. It’s driving so much better.
 

And the OCV also fixed the rough idle and acceleration issues. The car drives perfectly but I still have codes which I have yet to scan again. I’m going to do that when I leave this AA meeting. I’m super low on money for a couple months and I’m enrolled at AZ automotive institute so they can reset the TCM for free I’m sure. All labor is free there, only have to pay for parts. Pretty good deal. I start today so I’m going to speak to one of the automotive instructors prob today or tomorrow. I’m enrolled in a welding program so it won’t be one of my instructors. But I plan on having them do a LOT of work. Free motor/tranny swap labor will be nice. 
 

https://vehiclefreak.com/how-to-reset-a-subaru-transmission-control-module/

im thinking this link above is for an older Subaru, but I would think there is a similar procedure for 4th gen LGT. I installed a used TCM since it didn’t need to be reset or programmed. But to get the code off I’ll ask the school if they can do that for me. They should have everything for basically all cars to be repaired being as it’s a very reputable school in Phoenix. 
 

so I had this really bad rattle coming from the “engine” and I thought the OCV would fix it. It made it a lot better due to smoother idle, but not completely better. Today I realized that the battery is held on by the down straps. So I pushed one of the hooks and voila, it went away. So the car drives great now and no more rattle. It was so loud and i thought my car would crap out on me any day. Like it was so bad. When I was at idle it would “click” so loud and was getting worse and worse. So I tightened the strap and it’s gone.  I couldn’t figure it out for the life of me but finally fixed that. The car really drives very nice right now. There was a broken vacuum line above the OCV that connects to the IM and goes over to some valve above and slightly left of the fuse box. So I fixed that today. I think that was part of my idle problem and prob my accel prob too.

 

ok enough ranting and the gist of what I said:

 

TCM needs to be reset via A laptop with the software and proper cable in the above posts. Or let my school do it. Code won’t turn off on its own by fixing the problem with a USED TCM. I hope that works cuz like I said car drives/shifts perfectly now but codes still there

 

 

Thank you for all your help. I appreciate it very much!

 

 

edit- my SurePost package came a couple days earlier then expected! Still took a while like 5/6 days. But yeah the transfer to USPS is a pain and waste of time. Luckily they delivered on a Sunday and came 2 days early!

Edited October 17, 2022 by 3rd4thGen

[samwe]

it sounds like you got this solved, bit for anyone else who comes across this thread I thought I would add my experience with using a different year trans.

I put an '06 5EAT in my '05. I had codes so I got an '06 TCM and used FreeSSM to reset the TCM and everything was fine after that.

Edited July 23, 2023 by samwe