2017 Leaf won't fully turn on

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Driver8

Well-known member
Joined
Sep 29, 2020
Messages
79
Location
Seattle
So twice now in the last week I have attempted to use my 2017 Leaf (owned 2 years) only to have the car not fully turn on. I don't get the normal startup screen, and it continues to give me the "Brake + start button" message (even though I"m pressing the brake when starting). Almost all the indicator lights are on, and the driver's window doesn't appear to work, but the other windows do. I read to give it a quick charger plugin, but when I plug the charger in I get one beep, and none of the blue charging lights come on. Eventually I have been able to get the charger to turn on after a few plug in attempts, and then the start up is normal. Charge on the battery doesn't seem to be an issue as it has happened at both 40% and 85% charged.

The accessories and lights still seem to work during this false start, so I"m not sure it's an issue with the 12V battery.

Any thoughts?
 
The accessories will still work at a voltage that won't start the car, so eliminate the 12 volt battery first. Check its voltage with a multimeter, or plug it in to an external 12 volt charger for a few hours. The car is the right age to have an OEM accessory battery that is failing from age. If you do have to replace it, I recommend an AGM battery. The correct type is 51R, and the R is important. They cost more but are likely to last longer. Get a real, brand name battery, have the auto parts store fully charge it before it is installed (or do it yourself).
 
The main high voltage battery is disconnected when the car is turned off. The 12V battery is used to power up the computers and relays that activate the high voltage battery when the car is started. Once the car is running, the 12V accessories are powered by the DC-DC converter so at that point the 12V battery isn't absolutely required.
 
Driver8 said:
On a somewhat related note (and a naive question), why do EVs need a 12V battery?
A better question: why do EVs need the same 12v battery as an ICE car (because that's basically what they put in a new EV)?
And the answer is: they don't! Now you can go read all the 12v battery threads and think about putting in a smaller/lighter/lower capacity Lithium 12v battery.
 
goldbrick said:
The main high voltage battery is disconnected when the car is turned off. The 12V battery is used to power up the computers and relays that activate the high voltage battery when the car is started. Once the car is running, the 12V accessories are powered by the DC-DC converter so at that point the 12V battery isn't absolutely required.

And once the DC-DC converter is running, the 12V battery is still useful as a buffer to keep the 12V supply "clean"; i.e. steady and free of spikes and ripples.
 
As an update to this post: I was recently out of town for a week and we had a number of cold days in Seattle, I came back after the car not being used for 7 days and it wouldn't start and I got a variety of weird dashboard lights, including the "T/M system malfunction" message. I went to Costco and got a new 12V battery. After a very easy battery replacement, it looks like everything is fixed! Thanks for the advice on here!

On a side note, I believe this is the first time I have opened the hood on my Leaf in over 2.5 years of ownership!
 
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