Car wont start, battery current sensor at fault?
 

so , my project 2017 BRZ has been sitting for a bit, with a partially dead battery. usually when i need to move it or at least once every 2-3 weeks ill top 0off the battery with a charger, turn on the car and then let it idle for a bit.

this weekend i was going out to do some work on it, and needed to put it up on ramps. the battery had a lower charge but the car still started up and was doing fine. now its been a bit since its moved and it has an aggressive clutch (ACTHD) and of course my dumbass staled it. the thing is, after that, i tried to turn over, it did once and then nothing. thinking it need a better charge i hooked up the charger to top off the battery (btw its an Odyseey PC680).

came back to the car later in the evening expecting to just get back to work and start it up.. NOTHING, full electrical dead. now the battery is showing 13.52v across the terminals, even with dead cells it should energize the dash and show lights, etc. but nothing. i hooked up a spare battery in parallel incase it just needed a bit more juice. nothing.

but now is where it get weird. if i ground the negative terminal directly to chassis (using jumper cables) be it the odyssey or the spare battery, it will energize up the car, dash lights, power windows work, alarm etc.. so oddly enough it has to be something on the negative side of the OEM harness.

the ONLY thing i see that is there, that a "normal" car does not have, is the little black module at the base of the terminal. from what i can find it is the battery current sensor. from my quick 10 min looking through google results, the sensor talks directly to the ECU, but it should not cause any sort of disconnect if it fails. should only cause faulty reading and poor charging system operation. but what ever is on that short negative path, its acting like a full disconnect.

so 2 questions, have any of you had issues like this occur before? and does anyone KNOW if the battery current sensor fails, would it actually cause an open in the circuit and cause the car to be effectively electrically dead?

I'm sure i could bypass the stock wiring and just ground out the negative and start it that way, but i would rather avoid doing that if it could cause other issues.. of which i am suspicious of as i recently had to replace my alternator as the original one effectively burnt up the regulator. and I'm wondering if these two issues are related.

thank you in advance for any assistance rendered.

I am not an expert in electrical, but have you checked for parasitic draw? Aftermarket radio?
Dashcam?
Radar Detector?

What do you have plugged in?
When did this all start?
Intermittent issue or ongoing?
ETC

Have you tried replacing the negative battery terminal?

not much currently hooked up that could be a parasitic draw. (yet) part of what i was setting up to do was install some gauges.

the issue of it not starting, full electrical dead is new.

using jumper cables i did test that with a separate negative connection it would indeed energize. fully replacing the negative terminal is a possibility, though I'm trying to avoid just replace replacing parts. preliminary pricing that i pulled up for the sensor (part of the 2017 factory negative ground) was around $188.

I understand not wanting to just throw parts at it. I did see the neg cable on Ebay for $60.

Id check grounds before replacing the negative terminal.

OP can you send a pic of negative terminal ? The best you can of course!

will do, as soon as i get back from work!