Replaced another Frontier ECM today. You may know they're "popular" parts. Our Parts Department even stocks a few of the numbers for Frontiers and older Pathfinders, despite how expensive they are. What you may not know is why they're popular. Like a lot of people, you may think it's just a weak unit that's prone to failure. One day you turned your lollipop key in the ignition and the thing cranked endlessly, the code reader showed no engine present. The truth is, it's the same Hitachi motherboard used on a zillion other Nissans with ECM's that don't fail. So what's up with Frontiers, Xterras, older Pathies, and to some extent older Titan/Armadas?

Here's a link to a picture of what's up. It isn't the one I replaced today, which actually had green mountains growing all over both battery lugs. But it illustrates the underlying problem:

https://drive.google.com/file/d/157JkHk ... sp=sharing

Here's the explanation: There's a good chance that when the shop replaced your blown ECM, they also told you your battery terminals were badly corroded. When a battery "hot" terminal gets bad enough, it can spark when you try to crank. It tends to happen more often with lollipop keys and not I-keys, because an I-key BCM will "drop out" and abort cranking when the voltage falls way off. With a lollipop key, you're in charge of how long the engine cranks. You may not hear the crackle inside that corroded terminal, but essentially the starter is making connection with the battery through an air gap. This doesn't make the weeny little sparks you get when reconnecting a battery. This is a 200 amp monster trying to feed a starter motor, and 200A times 10 cranking volts equals 2 kilowatts of energy. Like any spark, it also produces huge electromagnetic spikes (EMF) that can reach 18,000 volts. You wouldn't want your finger to be in the way, and your ECM won't like it any better than your skin. On vehicles with a short, straight electrical path to the ECM, there's a good chance the lightning protection diodes will be overwhelmed and melt. Game over.

It happens less on say, old Maximas, because they have a half-loop in the wiring around the battery that offers some protection. Not to say it can't happen on other vehicles, but they aren't infamous for ECM failures like Fronties and Xterras. We also see it sometimes with backyarders using parts store terminals that don't fit right, trying to avoid a trip to the dealer for a proper replacement. Even if your dealer is a pirate, those terminals are under $20. Don't avoid.

Some of you know I'm the electrical guy who is always harping about grounds, but this story has a simple-but-different moral: Don't neglect the "hot" side of things either!

Wow. Super-interesting.

I wonder how many of these vehicles have begun the downward spiral to the boneyard for this very reason?

Great info!

A great PSA!

Thank you for sharing that info!

EMF is no joke. I used some resistor-less spark plugs in my Miata for better spark, and it ended up making my crank angle sensor go crazy. I data logged it and it showed me oscillating from 3,000-12,000 rpm with a period of 30 hz or so. Needless to say, the ECU didn't like it and it caused some pretty big drivability issues.

PapaSmurf2k3 wrote: ↑

Tue Jan 05, 2021 12:03 pm

I used some resistor-less spark plugs in my Miata for better spark, and it ended up making my crank angle sensor go crazy.

And that's just the tiniest fraction of the energy in a hungry starter-motor spark!

Yeah I wonder if you could develop a shielded cover/case for the ECM to prevent this sort of thing.
Ideally it should be that way from the manufacturer, but I could see it being a solid aftermarket "upgrade".

PapaSmurf2k3 wrote: ↑

Tue Jan 05, 2021 1:05 pm

Yeah I wonder if you could develop a shielded cover/case for the ECM to prevent this sort of thing. Ideally it should be that way from the manufacturer, but I could see it being a solid aftermarket "upgrade".

Won't work, Papa. The problem is, the EMF isn't all being broadcast. A great deal of it is transferred straight through the wires to the ECM backup pin. Like all high-energy sparks, the peaks are often picoseconds long, too fast for the protection diodes to clamp off. If they do manage to clamp it, they often melt because of the extreme voltage. Electrically, it's pretty much a catch-22. The best idea is not to let it happen in the first place.

Damn non-broadcast EMF!
Gets you every time.

PapaSmurf2k3 wrote: ↑

Tue Jan 05, 2021 3:46 pm

Damn non-broadcast EMF!
Gets you every time.

I know, I know, most people think of EMF and EMP in the same sentences, but EMF just stands for "Electro Magnetic Force". It's the friendly dragon that drives your motors and makes your sparks, until it decides to breathe fire and blow up your electronics. It can be a field inducing current in a wire or a loop of wire creating a field. The bad broadcast version is more properly called RFI, or Radio Frequency Interference. When it makes it into a wire it's properly EMI. Regardless of the how and why, what's important is what happens when there's way to much of it. You can easily weld with a 200A spark. 'Nuff said!

It's been a while since I followed anyone's posts with as much eagerness and rapt anticipation as VStar's...

Brother, keep 'em coming. If all my profs were as engaging and plain-spoken as you, I'd have nailed down a couple more degrees.

AZhitman wrote: ↑

Wed Jan 06, 2021 8:22 pm

Brother, keep 'em coming. If all my profs were as engaging and plain-spoken as you, I'd have nailed down a couple more degrees.

Psssst.... just between you and me, "Professor" is my nick in the shop.

Oops...

No surprise there. Well-deserved. So proud to have you on the team, sir.

AZhitman wrote: ↑

Wed Jan 06, 2021 9:25 pm

No surprise there. Well-deserved. So proud to have you on the team, sir.

Great to be here, this is a terrific bunch and a great site. Hope I can find the time for lots more!

Interesting. I assume you're talking about the VQ40 Frontier, Xterra, and Pathfinders? Thankfully I haven't faced this issue or known anyone that has, but it's something i'll make note of now if the issue ever arises. We have my Pathfinder(with 176k) and an Xterra(with 130k) in the family.

Kompresshun wrote: ↑

Sat Jan 09, 2021 1:24 pm

I assume you're talking about the VQ40 Frontier, Xterra, and Pathfinders?

Yep. V8 Pathys too, as well as any engine in the Frontier. They all have that same, short, straight wiring path between the ECM and battery.

What about D22s? Because I've been looking at my negative terminal, and it's starting to get a little wild looking!

Dattebayo wrote: ↑

Wed Jan 13, 2021 8:04 pm

What about D22s? Because I've been looking at my negative terminal, and it's starting to get a little wild looking!

The negative won't cause huge spikes like the plus side because much of the power and voltage has been sapped by the starter, hence the total wattage is a lot less. But it can cause lots of other issues like warty coils. See this thread:

topic628130.html