Long time no see everyone!

Well, the perfect storm has finally brewed, resulting in me having an 06 sedan with a blown transmission, and an 06 coupe with a bad wire harness/ECM/motor. I'm looking to utilize the sedan as a whole donor to the coupe, as they are both optioned identically. Here's the rundown of what I'm working with:

The coupe had suffered from a catastrophic electrical issue resulting in the ECM blowing out (and some o2 sensor wires suspiciously cut/dragging the ground) and the motor (finally) letting go whilst attempting repairs. We traced the issue to something related with the engine wire harness, as that is the only thing (we think) that could have been causing every ECM we put in to blow. Everything else is perfect on the car, good trans, solid suspension/wheels, everything interior electrical related is solid.

The sedan has suffered an issue with the radiator that allowed all the ATF to leak out of it, and long story short the car is unusable for the time being (NOT going to use the trans out of the coupe for various reasons). Motor is fantastic on this car however, and everything electrical is well sorted.

What I would like to know is the specifics regarding swapping the wiring harness. From what I read here it appears as if everything is the same on the surface level, and most importantly I have no idea what to swap over to basically guarantee that the ECM won't blow out on first start up. I'll be swapping the ECM, BCM (only if compatible), and ignition assy from the sedan over to the coupe as well so I don't have to fight with NATS. Is there anything I could be missing here? Any and all help would be awesome!


EDIT: I will also be getting a replacement engine bay harness as well out of a running coupe (not the engine harness the bay harness)

 

Honestly I would start looking at the IPDM if you were blowing multiple ECM, that's what feeds it power. Everything else is essentially power from the ECM going out to various actuators, sensors, etc with some data being returned back.

Also verify your alternator didn't crapastrophically die and start delivering 20v to the system. It's been known to happen and will quickly cook electronics.

 

Hey Cleric,

The previous shop has replaced the IPDM multiple times. Once with a verified working unit out of my sedan (I threw a junkyard IPDM in the sedan after swapping which works great!). and another time with a verified working unit off of ebay. Long story short the o2 sensor plugs were crushed and dragging along the ground, here's a link to my previous post about the coupe ( https://g35driver.com/forums/engine-...e-harness.html ). As you suggested I tore down the bottom end of that motor a while ago and found some rust INSIDE the damn motor, and it will be cheaper to just swap the motor at this point. We also found that the power rails on the IPDM board going to the ECU became oxidized after every ECU fried. I've decided just to take my totaled sedans wire harness, motor, and ECM and throw it in which in theory nothing else SHOULD be causing a short powerful enough to fry it after we swap correct? I've studied the wire harness and I cannot figure out if there is anything in the interior harness that could be shorting it out. Electrical s**t is not my strong suit as is most painfully obvious lol.

Thanks for all the help you've provided in the past man, you're a literal living library of knowledge!!

 

You might have a weak ground on the ECM, it's located behind the glove box near the ECM. As for scorching the buss inside the IPDM.... sort of making me think something failed inside your fusible link and a fuse isn't popping when it should. See if you can wrecking yard salvage another fusible link complete with all fuses.

 

Gotcha, I'll check that out. In theory swapping everything over from the sedan that is compatible will fix the issue correct? Just making sure all my bases are covered.

 

Update, swapped EVERYTHING over and it runs! Engine, engine wire harness, ECU wire harness, and engine bay harness. ECU and the immobilizer got moved as well. Car is 100% again!