I’ve had unknown draws before and many times they’re not constant draws. A constant draw is easy and quick to find. A draw that only happens when some module or other wakes up is a lot harder to find.
I recently watched a YouTube video from someone who'd tracked a nasty intermittent parasitic draw [0]. The problem only happened after turning the ignition on & back off (so the standard test of disconnecting the battery & reconnecting via the ammeter wouldn't show it), and the draw cycled between 3.6A and 0.3A.
Also, after turning the ignition on & back off there were a lot of (normal) transient draws (from things like the dome light that don't turn off immediately). Even with the problem circuit disconnected, it drew around 6A (!) immediately after the ignition was switched off, dropped to 0.4A after about a minute, and sat at that level for another 9 minutes before dropping again to 0.06A. That means if he hadn't waited ~10 minutes per test, he'd have been chasing draws that were actually normal.
Combine an intermittent fault with intermittent normal behavior, and you've got a troubleshooting nightmare.
As an example, my 2017 Corolla runs the fuel pump for a while 5 hours after shutdown to test fuel system pressurization. I didn’t even know until I recently started parking it inside and I finally heard it running.
I learned about this with my 2013 Scion iQ. I was living with my brother who didn't allow weed smoking in or near the house so I would go hotbox my car.
Weirded me out the first time I'm sitting there in silence smoking a bowl and suddenly fuel pump noises. Which were easier than normal to hear because I took the back seats (the only sound deadening in the back) out of that car so I'd have room for a full size spare tire instead.
With my current car (2020 Kia Sportage) I've noticed the head unit is waking up before I even start the car. As soon as you unlock the car I can see my flash drive light up with activity as the head unit gets ready to pickup music from where it left off.
Yeah that's pretty normal across different manufacturers, and you only hear it if you park in a quiet garage and happen to be in the garage at the moment it turns on to do it's thing. It's testing the seal of the fuel cap to make sure you aren't just venting gasoline fumes.
I had to sleep in a work truck once and every hour or so it would modulate the shutters in the air vents to refresh the air in the cab or something. The click and buzz whir kept waking me up, it was quite annoying.
Yes. I had a Dodge Charger where the parasitic draw wouldn't really become problematic until 3 days after you re-attached the battery. At which point it would be so bad it would discharge from full to empty overnight. It could even out-draw a trickle charger.
I took it to several mechanics who couldn't find anything - because they'd unplug the battery to add a meter into the circuit. They weren't willing to wait 3 days afterwards to come back to it.
I ended up disconnecting the battery overnight. Worked fine then. Traded it in; I feel a bit bad for the next buyer.
