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2012 MP4-12C 2018 720s
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GOT IT TO START! W00000T!

Ok, so I left the door open with a towel by the lock so it wouldn't lock while it was charging and not working. I never closed the door. I, thankfully and accidentally let the door close, cursed as I approached it to see if it would open. IT DID. and once it did the interior came to life. Then, when I hit start button, it started right up!

So I guess for whatever reason, if the door was up while the battery was dead, and you never close it, the computer for some reason stays dead/dormant. You have to risk closing the door at some point and that helps the car 'reset'.
For future reference, when you reconnect power the car locks. If you have folding mirrors turned on it will fold them when you give it power. I always do it windows down, doors closed (windows won't go up with power up) so everything is in a known state. When you unlock the car it wakes everything up simultaneously. Every time I see someone leave a door open while doing battery things it gets confused. At the minimum you can use the inside door release pulling it twice and it corrects the issue most times.
 
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At the minimum you can use the inside door release pulling it twice and it corrects the issue most times.
Can you clarify that?? Are you saying to unlock the door twice with the manual release to wake the car up? I thought I'd locked myself out of the trunk last week, but because of the power loss it had lowered the windows, so I was able to open the door manually and then use the manual trunk release (another reason to upgrade to a 570.... lol).

There's also a related behaviour when leaving the car parked with the door open. After a while it goes to sleep and the window doesn't go up until you press the key fob or start the car.
 

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2012 MP4-12C
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Discussion Starter · #65 ·
Can you clarify that?? Are you saying to unlock the door twice with the manual release to wake the car up? I thought I'd locked myself out of the trunk last week, but because of the power loss it had lowered the windows, so I was able to open the door manually and then use the manual trunk release (another reason to upgrade to a 570.... lol).

There's also a related behaviour when leaving the car parked with the door open. After a while it goes to sleep and the window doesn't go up until you press the key fob or start the car.
The 12C has the same manual trunk release process.
 
2012 MP4-12C 2018 720s
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3,161 Posts
Can you clarify that?? Are you saying to unlock the door twice with the manual release to wake the car up? I thought I'd locked myself out of the trunk last week, but because of the power loss it had lowered the windows, so I was able to open the door manually and then use the manual trunk release (another reason to upgrade to a 570.... lol).

There's also a related behaviour when leaving the car parked with the door open. After a while it goes to sleep and the window doesn't go up until you press the key fob or start the car.
Not the manual release, the door release on the inside, the one normally used to open the door. The related behavior is also resolved by the interior door pull twice. It's just waking up the car.
 
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Ok, so here is the mystery. The McLaren Jumper shows that the battery is like half full. What the heck? Why would the car go dead if the battery is half full?

What’s weirder still. The car still won’t start. It normally starts with way less charge showing there.

I’m going to assume it’s just inaccurate from the jump and give it a few more hours.
I am currently having the same issues like you and couldn't find a way to fix it. The difference I have is voltmeter shows 13.xx when Mclaren trickle charger is connected if not the car doesnt work and battery shows 1.5, 1.6 volts all the time. Car works with the help of Mclaren charger and doesnt pass %0 while driving with classic automatic parking brake problem exists. Car is not driven for so long and currently have 3 charges including original trickle charger , ctek and noco. Only Mclaren original charger comes up to 3/4 and gives error. I even saw it full but the battery in reality battery is not full at all. Any suggestions experts? I am guessing the bat is dead for good
 

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2012 MP4-12C
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Discussion Starter · #70 ·
I am currently having the same issues like you and couldn't find a way to fix it. The difference I have is voltmeter shows 13.xx when Mclaren trickle charger is connected if not the car doesnt work and battery shows 1.5, 1.6 volts all the time. Car works with the help of Mclaren charger and doesnt pass %0 while driving with classic automatic parking brake problem exists. Car is not driven for so long and currently have 3 charges including original trickle charger , ctek and noco. Only Mclaren original charger comes up to 3/4 and gives error. I even saw it full but the battery in reality battery is not full at all. Any suggestions experts? I am guessing the bat is dead for good
In my circumstance the car DID actually charge enough to start, but the ECU did not restart because I had the car door open the entire time without closing it (since I had to “break \into the car manually when the battery was dead, I didn’t want to lock the door while I charged the car). Once I closed the car door, and left the car alone for a while, that restarted the ECU and the care came alive and let me start it.

Im not sure if you have a similar issue or a different one.
 
2012 MP4-12C 2018 720s
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3,161 Posts
I am currently having the same issues like you and couldn't find a way to fix it. The difference I have is voltmeter shows 13.xx when Mclaren trickle charger is connected if not the car doesnt work and battery shows 1.5, 1.6 volts all the time. Car works with the help of Mclaren charger and doesnt pass %0 while driving with classic automatic parking brake problem exists. Car is not driven for so long and currently have 3 charges including original trickle charger , ctek and noco. Only Mclaren original charger comes up to 3/4 and gives error. I even saw it full but the battery in reality battery is not full at all. Any suggestions experts? I am guessing the bat is dead for good
That's sounding like a bad battery. I have one in my shop that acts the same and I'm going to spend time fooling with the battery to see if I can make a solution.
 
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