Car rocking when completely shut off, then alarms going off

Tiny
SHEWASBORNTORIDE
  • MEMBER
  • 2013 HYUNDAI SONATA HYBRID
  • 2WD
  • AUTOMATIC
  • 122,000 MILES
My car has completely scared me twice now. My car will be parked turned off and this happened only twice but when I was in front of my car about 10 feet away my car started rocking (yes park is on) and the trunk opened the alarm went off and then I freaked out. Because my car rocked hard (I pushed it and couldn’t mimic that rocking) so I ran into the house grabbed my keys and unlocked the car and the battery was dead with a brake warning going off on the dash. I charged it with a jump starter (took 1 minute to make the car react) and the car worked great. I ignored this strange thing after a mechanic visit where all is fine. Then it happened again right after I came home tonight. What can this be?
Thursday, February 20th, 2020 AT 8:39 AM

3 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Are you saying it rocks side to side or it is rocking front to back? Not that this would change my opinion but it will help me understand what it could possibly be.

Clearly I have never seen or heard of a vehicle that starts rocking on its own enough to set the alarm off and the trunk opens.

Is it parked outside when this happens? Were there strong winds, earthquake or some other possible explanation?

Unfortunately I am as stumped as you are on this one. The other experts will read this as well and chime in if they have any ideas.

The only thing I could possibly imagine is it is rocked front to back, that the parking brake slipped and it rocked forward and the parking pawl caught it causing it to rock. If it did this hard enough, it could pop the trunk which is what set the alarm off. This would have to be a serious set of events but I guess anything is possible.
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Thursday, February 20th, 2020 AT 5:01 PM
Tiny
SHEWASBORNTORIDE
  • MEMBER
  • 2 POSTS
Yeah it was back and forth. There was no winds or anything cause I was taking care of some bottles that needed recycling and they were on the ground while I crushed them and bagged them. I was scared of my car even though it’s apparently fine.
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Saturday, February 22nd, 2020 AT 9:13 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
I am not sure how this would happen because when the engine (batteries in this case) are not on the vehicle should not be moving because none of the components have power in order to move.

The only possible thing I can think of is because this is a hybrid that the parking pawl that locks the transmission in park so it can't roll doesn't fully apply or slips due to it being applied electrically. This would allow the vehicle to roll forward and then when it does, it fully engages causes it to catch in park and it would stop rolling abruptly making it rock back and forth.

That is a stretch but I am not sure of any other explanation. Sorry I can't definitively figure this one out for you.
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Sunday, February 23rd, 2020 AT 8:18 AM

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