Intermittent complete electrical failure - Bad BCM?

emaurey

Hello,

I got a complex electrical problem with my Z (09 370Z 6MT 62k miles) and worse it only happens about once a week, and never when I bring it to a shop. Hoping someone here might have heard something like what I am going through or can help run through diag.

What happens is that very occasionally when I turn off the Z, it completely dies. No dome light, gauges go completely dead (no red needles), doors wont unlock, no annoying beep that my lights are on/key in the dash. The start button also has no light on LOCK and the car will not start up again. I have tested the battery in this condition, full 12.6v at the battery. Over time, various parts of the car start regaining power, but I have about 3-5 minutes of what I can best describe as a "brown-out." The dome light will flicker, the door will try to unlock but just click over and over. The ignition button will eventually display Lock, but pressing it will only cycle to ACC, then power off with a flash of the gauge warning lights. Sometimes it will cycle to ON but not start the car, just attempt to do so then power off completely again. Once I go through this electrical hell, the car will eventually start and be perfectly fine for days as a daily driver.

Additionally once in a blue moon I might experience some issues in the first few minutes of driving. The lights will flicker, gauges die, car stutter for a brief second. When this happens its pretty much a guarantee that I will experience the power off issue when I'm done with my drive. Also during this drive I do notice my voltmeter swinging between 13.5v to 15v as if its tied to my tach.

This has been going on about a month and a half, not getting better or worse. I didn't do any service/repairs before this started. I can identify any pattern of when it happens (not rain/water related or other drive conditions).

Already have taken it to 3 shops (two dealerships), verified battery condition, ground cables, harness connection points, ran diags on the modules - nothing came up.

My best guess its a failing BCM, but that's a repair I'd rather not make without confirmation. Anyone have any ideas on what could be causing this issue/how to confirm a bad BCM?