I installed an under-seat powered sub using output/speaker level for input and auto-on switching. Install went well and unit played fine with car not running. I was concerned the Boss inline fuse at the battery terminal was not as tight as possible (8 ga wire seemed closer to 10 ga), but was not getting hot or causing any trouble. I buttoned things up and was a happy guy.

Then I went to START the truck. BOOM - out go the lights!! TOTAL loss of power as if a fusible link had been blown. After about 10 minutes, power gradually came back, including headlights etc.. Stereo still working fine with engine off. Another attempted start - total crash again. After scratching my head and poking around, I realized it was the ECM shutting down and slowly resetting itself after about 10 minutes. So I actually reset the ECM by disconnecting the NEG terminal on the battery for 30 min. Hooked back up, tried to start - CRASH. So I disconnected the sub power tap at the battery and repeated the process - SUCCESS!

I investigated all of my wiring and grounds, and felt the 8 ga attachments at the inline fuse were not tight enough. I doubled back the exposed wire(s) and pushed that into the socket and re-tightened firmly. I was able to really crank down the grub screw now.

Long story - that mediocre cable connection was the issue! Truck started right up and has been working fine since. My question is, anyone know what the ECM was detecting to shut things down in a panic? I assume as the START circuit was engaged at the ignition, some kind of current/voltage fault (spike/drop) was detected by the ECM when the sub switched on (with the stereo speaker output). I assume even direct switching from the head unit or other source would have acted the same way. anyone else ever have this issue? Thoughts? Condemnations?

Does anyone have knowledge of how the computer senses this stuff and what the thresholds are for tripping the ECM off?

No. We do not.. The ECM are mostly rock solid in the 3rd gens and we don't mess with them.

The ecm isn't super complicated and probably senses the voltage level as a guess.

Sent from my SM-A536V using Tapatalk

Well, I hope passing on this incident will help non-start troubleshooting. Don't just check your battery connections, but check all high-draw connections.

That was a weird experience indeed. I would expect that kind of thing happening on a CANBUS system.
The 3rd gens, I know of my 2000 is just traditional simple wiring.

I know bad battery connections do strange things but, total system loss due to a loosely connected amp wire? I'm curious what were the electrical mechanics that led up to that loss.

It seems like it was a bad battery connection but, just simply removing the amp power wire solved the issue. And clamping down on the wire solved the system loss while the engine is running.

Curious to hear what the collective have to say about this too.

#1 rule in electronical troubleshooting is check all connections and fuses. Did you find the cause of your non starting issue?

#2 rule of troubleshooting if you messed with it start where you changed or added things.

Sent from my SM-A536V using Tapatalk

My first thought was that because I had been playing the stereo for a while, I had run the battery down and wasn't getting proper voltage. I have a good battery load tester that showed the battery to be in good shape. Regardless, I charged to battery to full charge make sure that wasn't the issue. Made no difference. Computer still crashed upon trying to start. At no time did the engine ever crank - just a black screen of death from the instrument panel when I hit START. Then 10-15 minutes and the computer would reset.

Perhaps it is a relay (faulty?) in the starting system that tells the computer to shut down. For instance, to reset the computer without disconnecting the battery terminals fo 15 minutes, I found online I could pull the R7 (? - I forget) relay and reinsert and the computer would reset.

But sleeping on the issue overnight, I realized it must be in the loose connections in the fuseholder causing some sorta fail-safe fault in the system. Just never had it happen to me. It has been functioning fine since improving the connection. I also ordered some copper connection furrules to enhance the two 8 ga connections and keep them from loosening.

Yes - the cause was a poor connection in the fuse holder causing excessive draw when the subwoofer turned on at the same time the START circuit was engaged. With the stereo off, the car started fine. But with the stereo on, the draw from the sub caused the computer to "fail-safe" and shut down. As soon as the connections in the sub circuit were improved, the vehicle started fine.

I just wanted to mention it here in case someone else was having similar trouble. Seemed like the connections were good, as the system played fine, but apparently the draw was too much at startup.

Great news, you got it fixed. You are probably correct on the relay not having the proper voltage to pull on and activate the contacts. As these ECU are older tech. They weren't super complex and rarely failed.

Also, good job in coming back to the thread to post a solution. So that if other members have a similar issue this may help them..

Sent from my SM-A536V using Tapatalk