ECU let out the smoke

[tatsuo8088]

Hello everyone,

So I have a weird situation.  I have a 2005 Legacy GT wagon whos ECU decided it wanted to BBQ
(pics below).  I also included pictures of a non-BBQ'd ECU from ebay to compare, and from the looks 
of it it seems a mosfet caught fire and took out a diode on the backside of the board. 

The back story, I had just registered the car after a year of putting it back together and wanted to daily it to test. For 4 days
the car was running great, and no codes.  The day the ECU let the smoke out, I had driven it around and
parked it a couple times to run a few errands.  I then decided to go to the hardware store, and at the hardware store
turned the key, no crank, Er HC showed up, and smoke coming from the ECU.  I immediately ran to unhook 
the negative terminal.

Some history, the car had a blown turbo and was given to me because the previous original owner 
didn't have the time to work on it anymore.  So I replaced the turbo, redid some seals, replaced
the turbo intake pipe, and replaced the intake manifold because the pressed in threads stripped out.
The car has been sitting for 7 years before coming into my ownership. To my knowledge, the car is stock
other than the addition of an aftermarket alarm with remote start.

I have a couple theories as to what happened.
1. The ECU just failed because its been sitting in a relatively humid environment in Hawaii.
2. I accidentally triggered remote start couple days prior to it not starting and started a chain of events
3. I have a short in the harness somewhere.

My plan of a attack is to reattach the battery, and test every pin for 12v where there shouldnt be. 
Other than that, are there other tests I should run?  
Can a short cause damage like that?  I would think I would get a code or trip some sort of protections with-in the ECU to prevent such damage.
Lastly if anyone can tell me what circuit that mosfet belongs to would greatly help in narrowing down a circuit to test.

Thanks

[KZJonny]

Yikes. Can't be of much help to you on the electronics end of things, but I do know a guy who's parting an '05 GT wagon (AT). If you don't find something local for a decent price, I'm sure I could ask him, if you have an automatic.

Cheers.

[tatsuo8088]

Thanks for the offer KZJonny, but I have an ECU ordered from Ebay for about 100 bucks, so not bad.

 

Update:  I noticed that one  of the ICs looked like it overheaded.  So now I guess I'm more confused as to what lead to what.

Edited November 5, 2022 by tatsuo8088

[m sprank]

I have "pin outs" for the connectors, but no engineered drawings of the actual trace pathways.  There are a very few people with that level of knowledge.  Bill Knose (Delicious Tuning) does, but he probably wont share as he makes money off tuning old "un-tunable" ecms by flashing the onboard memory and reprogramming the ecu.  If it sat for years in HI, I would immediately blame the environment as your situation is rather unique.   

[tatsuo8088]

Thanks m sprank.  

So I guess would I be correct in assuming that there is no short in the wiring harness?  I would think that if there was one, a fuse would have popped or the car would be running bad followed by a check engine light.  

Before the car failed to start, it was driving perfectly.  I had a scan tool attached to monitor what was going on, and nothing felt or appeared out of the ordinary.

[m sprank]

Fuses would have blown, or a CEL would have triggered prior to the magic smoke leaving the Genies bottle.  I completely submerged a "live" LGT ecm and nothing like that happened.  Car even kept running.  Sucked drying out the carpet, lol. 

[tatsuo8088]

Cool,  this makes me feel better about putting in another ECU.

[m sprank]

You can swap ecms. However, they must be same model year and trans. Also, you will need the corresponding body integrated unit and ignition tumbler.  You can reprogram, but would most likely need to tow to dealership. Car will not start as ecm does not recognize the chip in key.  

You will have two keys. One to open the doors and trunk and one for the ignition. 

I would also check the tune file to make sure you have the correct tune and not a modded ecm file. 

Edited November 13, 2022 by m sprank

[tatsuo8088]

I bought an ECM that was off a 05 Legacy GT, with automatic. Same part number but with a D revision instead of a B. 

If I'm understanding correctly I won't be able to marry the BIU and ignition tumbler on the car to the replacement ECM? 

[Infosecdad]

There are three options with a replacement ECU.

1. Get a dealer to reprogram the replacement ECU to match your VIN

2. Physically desolder and move the chip that has the VIN in the eprom from your old ECU (assuming the eprom is still ok)

3. Pull some electronics together and read the VIN codes from the eprom and write/update the new ECU.

 

Not sure if the old one has damage to the eprom chip that's used for security, if so, then getting a dealer to reprogram may be your only option.

[tatsuo8088]

Thanks, that was the plan to tow it to the dealership and program the replacement ECU to the car. 

[m sprank]

Call the dealership(s) first.  No local dealerships in Cali would perform a reprogram when I had my shop. Thats how I know about the parts required to do it yourself. No tuner I know of can marry an ecm and biu. When my shop was open the tech was unavailable.  Dealerships were notorious for refusing to perform work on modified cars or anything outside their day to day norms. 

[tatsuo8088]

Update

I found someone local that was able to desolder the eeprom from the dead ECU and solder it on to the used ECU.  I installed it today and started it 4 times to test.  So far no smoke was let out, and the car runs perfectly as it did before.  I did a code scan, and no codes.

Fingers crossed that this was a one off event.

Thanks everyone!

[m sprank]

Going all out. Glad its working for you. 

[Infosecdad]

On 11/14/2022 at 6:15 AM, m sprank said:

Call the dealership(s) first.  No local dealerships in Cali would perform a reprogram when I had my shop. Thats how I know about the parts required to do it yourself. No tuner I know of can marry an ecm and biu. When my shop was open the tech was unavailable.  Dealerships were notorious for refusing to perform work on modified cars or anything outside their day to day norms. 

Just for reference, I ran into similar issues which led me to writing up how to go with cloning the eeprom chip.

The one dealer that would agree to do it, said they would charge me $400 and would make no promises it would work right. As it was 2.5hrs away, I had no desire to gamble to that level.

Glad to hear you found someone that could help out with the soldering, and you are up and running again!