ECM interchangeability question

[Rattlenbang]

Hi all, I think I might have damaged my ECM by accidentally creating a short in my 2008 Impreza, and since I have a 2008 Outback, I'm wondering If I can do a quick swap to confirm? Same 2.5 NA motor and auto trans.

 

[Dick Foster]

It depends. If its a People's Republic of California car the ECU may differ. Also the trim level may or may not play a part. At least the engine and tranny and model year must be the same and have the same equipment ie air con and such.

 

[Rattlenbang]

Pretty much what I expected. KInda if it works it does if it doesn't it don't. But I guess the biggest concern is if it isn't a match will it/could it damage the outback ECM?

 

[bmart]

Compare part numbers.

 

[Raymond3006]

Pretty much what I expected. KInda if it works it does if it doesn't it don't. But I guess the biggest concern is if it isn't a match will it/could it damage the outback ECM?

YEP !
With "S" , it is a Crap-Shoot --- no-one ever knows for-sure until SOMEONE (you) step in to the Great-Beyond , all on your own !
And then return to your Home-Universe, and tell all the rest of the Walking-Talking-World what was on the Other-Side of the Great-Divide !

Their "science" is so much different than the Science we grew up with , it is not possible to know anything about their thought-process until after you try for yourself !!!

GOOD-LUCK , and dial US up after you get back in our Galaxy !!!!!

 

[Rattlenbang]

It was a very useful exercise. I started as safe as possible by putting the suspect Impreza ECM into the Outback and got the exact same symptoms: no crank, no start. Tentatively I then put the Outback ECM in the Impreza and this time got a crank but no start. It was also doing some click click stuff under the dash with key off.

I scanned the Impreza and the CAN bus error was now gone. Previously there wasn't communication between the trans and ECM nor with ABS. The whole line was down. And I could only get partial OBD communication to the ECM with two different scan tools.
The Outback ECM worked fine when I put it back in the Outback.

It occured to me that the ECM might have to be VIN matched with the Impreza to work; I've read that that is often the case when swapping ECMs in vehicles. But it still allowed me to troubleshoot the system.
I'm convinced the fault is in the ECM, but I suppose in hindsight it would have been useful to confirm by scanning the Outback with the Impreza ECM installed and see if I get the same CAN bus fault.

 

[Raymond3006]

You went after THIS like a Practiced-PRO !

You appear to be on the Right Track :
Now with this Test-Cycle behind you , it may be possible to expand your tests , and get more meaningful read-outs !
Let everyone know if you make more progress !

Just remember , each ECM is usually designed to Communicate with several Body-Control Modules , each of which is Make-Model specific ; so any specific BCM may give ERRORS , if it does not have appropriate interface codes , but most BCM's will try to function with most ECM's ..... , of the same Gen-Level of Vehicle. Start jumping around between Gen's and you may get into more devious results !!!

 

[Rattlenbang]

That's just the first hurdle. Now the used ECM will need to be cloned to the original one, as it holds VIN and key info. There are many options, none of which are perfect or necessarily very affordable. Dealer is ridiculously expensive because these ECMs are designed to prevent VIN swapping after the first VIN installation, so dealers want to sell a new ECM.
You can send the two ECMs in for cloning but it's still quite expensive, my cost around $500. You can use a Carpro clone to swap the data directly between the EEPROM chips, but it's quite complex and sometimes you have to actually physically remove the chip off the PCB before you can write data to the chip (which is why the dealer can't write to the chip themselves using their OBD2 tool).

You can physically swap the EEPROM chips - not a big deal as they are just surface-mount 8 pin chips, but apparently you can sometimes lose the Key data so it still won't start and you now have to hire a locksmith to recode it to your keys.

(Note that I suspect this data loss may be caused by the manner in which they usually remove the EEPROM chip - heat the whole thing with a heat gun until the solder melts. You've already got the data in your Carpro from the old ecu so it doesn't matter that you damage the data in this EEPROM. Once removed, the EEPROM is flashed and when it's remounted a soldering iron is use to quickly resolder the pins back on so it's much more gentle to the chip.)

Safest is sending it out, but most non-dealer expensive.

Less safe is buying a Chinese Carpro clone, which preserves the data of the damaged ECU. Problem is these things can be sketchy and have been frequently known to not work or even rarely brick your ECM (though this might be user error). At least you can get your money back!

Cheapest and quickest is to carefully and gently swap over the EEPROM chip and hope you don't lose data. If you do, still looking at hundreds for a mobile locksmith to recode the thing. (I recently had an all-keys lost situation that cost $600 to rekey by a mobile locksmith). Needing a rekey can make it close to the cost of just sending it in for cloning. But that could take weeks, and I need to get this back on the road. And I hate paying someone to do stuff I should be able to do myself.

Decisions, decisions.

Just found the EEPROM:

That's a tiny bugger

 

[Rattlenbang]

EEPROM REMOVED