Very weird thing happend this morning...

2005 350Z with ~153k miles. Drove to the office this morning (50+ miles at an average of over 50mph - so good highway cruising). I park, turn off the engine, but turn it off only enough to shut the engine off and leave the radio running for a few more minutes (like 5min or so). I was waiting for someone else to unlock the building, and it was taking a bit longer than expected, so I decided I would drive and get a cup of coffee or something, yet. I go to start the Z, and - nothing...like the battery had drained.

I hadn't been sitting there long enough for that to happen (like I said, 5min or so). So I pop the hood to double-check the tightness of the battery terminal connections, and I notice that the headlights are still on. I go in the car and make sure I turned the headlight switch off...which I did. I turned the switch back on (verified the headlights were still on) and then turned it off again (and the headlights were still on...I also verified the running lights were still on). Oh, and the battery terminal connections were tight. This makes no sense...the headlight switch is off...why were the lights still on?

A few minutes later my colleague shows up to unlock the building. *edit* I should add here, that while I was in the building the headlights did turn off (the battery drained down all the way?) *edit* We have a jump-start pack inside, so I grab that and go to start the Z and it fires right up. I leave the car run for 10min or so, rev the engine a few times...and then the ultimate test - turn the car off and try and start it again - and it works!

There are no lights on the dash, either, and everything seems to be working as normal. The voltmeter on the dash is showing a steady ~13.8V when the engine is running, too.

I'll be upfront and say that I should probably replace the battery at this point, anyway. I've been pushing it: I bought the car in 2018 and it had already been sitting for 2yrs - at that time I charged it overnight and it started up the next morning. The battery is from late 2015, and we are in 2023 now, so...yeah, it's due. Still, the drive to work should have provided ample charge time and it started this morning after sitting for more than a week with no issues. It was all just very odd.

 

Kudos for providing the minimum info (year milage, background) on your Z before providing details on your electrical issue. While I have no definitive answers for your electrical problems, pulling codes is usually the next basic task to try. Be sure to get a scanner that can also look at BCM codes. Our cars are getting older and any wiring issues (shorts, poor grounds, etc.) can result in some strange issues. I agree with you on the battery, however. It's served you well up to this point, but lead-acid batteries have a limited lifespan and yours may be up.

 

Any recommendations on a good scanner for the Z? I use a VAGcom/VCDS for my '04 VW Passat, and FORscan for our 2019 Ford Flex, a VIDA/Dice for our '05 Volvo V70R, and a Foxwell NT510 for our '05 Dodge Ram and '06 Mini Cooper - so I'm not unfamiliar with using these diagnostic tools for maintenance. I had been considering the Nissan Data Scan tool (https://nisscan.com/?v=7516fd43adaa), but haven't pulled the trigger on that, yet.

I keep my cars for many years and try and perform as much of my own maintenance as possible, so I find it worth the investment to have the right diagnostic tool.

 

I use an older version of UpRev's Cipher software to pull codes on my Nissans/Infinitis, but that's an ancillary tool for racing. There may be better (and cheaper) tools available, but it does the trick for my vehicle fleet.

 

You probably have a BCM issue. The BCM controls the healights. I'd just carry a jump pack with you in case it happens again. Also, something to try next time the headlights stay on... Try disconnecting the battery and re-connecting. If the headlights don't come back on, you're probably looking at a new BCM soon.

 

I went ahead and installed the new battery over lunch (Group 35 size Interstate from Costco with the 36mos 100% warranty). The car did turn over a lot stronger/quicker with it.

That's a good idea, to keep a jump pack in the car for a while - just to make sure there isn't something else going on (BCM issues, etc.).