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!