Hey all,

So my beloved former car (06 Coupe 5AT) recently came to me with a few strange issues. Whenever the new owner was driving it around it all the sudden cut power and would crank no start. The radiator fans were on and security light was solid red. Quickly realized that the ECU went bad and it took the ipdm with it. After replacing both of those the car ran just fine for about an hour before it did it again. I've inspected the wire harness in several areas and there are spots where it has either been cut or shrink wrapped together. My initial thought would be that it's just time for a new engine wire harness, but somebody on my local Facebook group told me that there is the possibility of the issue sourcing from the O2 harness.

Effectively what has been happening is something is causing the ECU to draw so much power that it is physically charring the 12 volt input on the ipdm for the ECU. The car has not had downstream O2 sensors in it ( yes yes I know ) for a considerable time. I haven't actually been able to get under it to check but I was wondering if any of you electrically minded guys had any input on the situation. It's been to the dealership and to a mechanic and nobody has seemed to be able to provide a sound answer.

Thanks!

 

The wires should never be burned (except from heat like near the headers) unless it's got the wrong sized overcurrent protection (fuses) installed somewhere.

Your initial symptoms were typical for an IPDM that's gotten wet as well as the sort of common "BCM had a stroke and forgot the key programming).

That said it's still never going to run correctly without those downstream O2 sensors, no timing advance, open loop fueling, probably missing 15-20% power.

 

Security light solid red is NATS/IVIS, that is the BCM not recognizing the key. It sometimes happens for no apparent reason especially after disconnecting the battery.

 

Gotcha. The burn I described was more of a very browned power contact going to the ecu. I'm going to go get a new BCM, ECU, and IPDM in the morning from the pick and pull as well as a harness. Should be a simple call to my key guy and get them paired together. As far as the o2 sensors I'll be putting some in whether or not he wants them, personally I believe it's ridiculous to not have them in. Looks as if the previous mechanic pulled those two timing cover ports off as well.

 

Well, didn't think I'd be replying so soon. This is what I saw when I took a quick peek under the car:


(Ignore the mask, I assume it picked it up while we were pushing it across the lot). Replacing tomorrow and throwing sensors in. Will update then.

 

Fortunately you can buy replacement harnesses for the O2 sensors.

I honestly wouldn't mess with swapping the ECM/BCM/IPDM until after the rest of the electrical issues are fixed unless you have EXACT replacements from another chassis. It needs to be another 2006-2007 coupe with the 5AT with the exact same options package (basically either it has a sunroof or it doesn't have a sunroof for the 5AT).

There was some minor differences between the 2003-2004.5, 2004.5-2005, and the 2006-2007 coupe, as well as the 2006-2007 RAS equipped coupe (6MT only had this option). Each had the option for 6MT or not, premium package or not, and each used a different ECM/BCM.

What is unplugged on the engine? Cam actuator solenoids?

Also, those harnesses hanging under the car are supposed to be clipped onto this bracket that bolts to the center of the transmission right behind the bellhousing at the bottom.

 

Gotcha. I was led to believe that an exactly same speced/year sedan could function as an electrical donor for the coupe. Found a few more trouble spots. The open ports on the motor are the lower 2 timing covers. I've attached pics of the areas of concerns. Of course I'll be replacing everything, starting with the o2 sensors/harness. Will update with progress later in the PM.







Thought I'd throw a thank you in there for Cleric. Seems like every time I come here with some new crazy problem with one of my VQs he has a great answer to give. Thanks for taking the time out of your day to help people like me out man!

 

Holy crap there's no covers over the water pump or chain tensioner!?!?! That literally lets debris go straight down into the oil pan. I think you should remove the lower oil pan and clean the oil pickup tube, it's probably got all manner of leaves and debris on it.

About those wires that are cut, do you have the cam actuators plugged in at the front/top of the timing chain cover? Do those other wires look like they plugged into an area near it but you can't find where to plug them in? If so it may have been originally a rev-up engine but someone put a regular non-rev DE in it. I know it has an AT right now but it might not have always been that way.

As for the computer compatibility, the BCM is mostly what's different in the coupe/sedan since it controls two extra windows/door locks. If you aren't buying a matched set of ECM/BCM they will need to be programmed to work with each other via Consult-II or Nissan Datascan2 with the BCM decoded. It's part of the NATS anti-theft system so you can't just plug n play a new ECM or BCM.

 

Yeah the mechanic that had it kept them off... for 2 months.... Seriously pissed me off when I saw it. Thankfully it wasn't ran with them off nor was it moved too far. No bolts to be found either. Yet another pick and pull item to grab. I'll get a paired ECU/BCM as well. The actuators are indeed plugged in, we're good there (well, had to plug them back in myself). It actually was my first car, I sold it to my buddy and he hasn't done anything with it except had this issue occur. It's a 06 DE 5AT, bought it as a 1 owner with 78k miles back in '18. The wire that is taped up is the remains of the side marker light, it got loose and was torn up by the belt causing the break lights to not work.