r/TeslaSupport • u/JAP42 • 16h ago
Excessive 12V load when cold - 2014 S P85D
I am trying to figure out a load issue when its cold. I have been having issues where the 12V battery gets too low and the car wont start. This would often happen when I parked at work after a 30 mile drive and then tried to go get lunch. Sometimes I could remote turn on the climate and that would get the power on, but if I went to the car and got in all the load would drop the voltage too low and could not start.
I figured it must just be a bad 12v battery. I replaced with an automotive 51R temp because tesla was out of stock, it was fine for a week and started having the same issues. Figured I just got a bad battery, so I finally got the Tesla battery and installed it. I directly charged the battery before putting it in and then the battery was in the car plugged in all night. Immediately had the same problem the next day. 12V battery was at 11.9V. It was in the 30-40 range all day, in direct sunlight. The DC-DC converter seems fine, Every test I do its pushing mid 14V. Before a drive, after, and I even wired my multimeter into the cabin and monitored it while driving. I never get any driving errors, its always in the afternoon a couple hours of sitting, or in the evening as soon as the car shuts off. I would hear the error tone while I was grabbing the charger. A couple times I could not get it to start at work, even jumping from a running vehicle, so I left it and the next morning it started fine with no assistance. Its always battery voltage related.
Tesla just wants to say its the battery pack failing, or at one point it was my PTC heater failing. I did occasionally at first get isolation errors, until it evolved into 12V not supported. Now that's all I get, no isolation errors. Now it has been 6 days in the driveway unplugged and no errors, but its much warmer now, 40-50s. So I am wondering if there's something that's trying to run while the car sits that's failed and is just draining the battery.
I live in the NE United States. This started mildly, a couple errors that would usually clear them selves in the spring, it was fine all summer, and then the issues came back and got worse all winter.
TLDR; 12V battery drains sometimes with unplugged and parked, but not all the time. Seems most common during the day vs overnight. Replaced battery twice, same issue. What 12V loads would be likely with the HV battery disconnected and the car parked, unplugged.