Car alarm is tripped when car has been idle in garage with no interference?

2018 HONDA FIT
53,569 MILES • 1.5L • AUTOMATIC
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APPLESTOANNIE
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Hi! I came here via your youtube video "How to Hard Reboot and Reset Your Car’s ECU" as I believe my 2018 Honda Fit EX has been having issues with the car's computer, but I wanted a personalized perspective given my car is newer than the demo car in the video, and my problems with it don't include a lock out.

I purchased the car used from a dealership a year ago where it went through a full 360 inspection. From there I got the transmission fluid changed to be safe given I know CVTs can be a bit high maintenance, and I've been changing the oil every 3 months.

For the first 6 months I had zero issues with the car, but over the last 6 months on 3 separate occasions the car's alarm has gone off while it's been parked in the garage alone--each time this has happened, no one has been anywhere around the car and it hadn't been driven in over 24 hrs.

During the first 2 instances, when the car alarm is turned off, all the engine lights begin to flash (as shown in the video attached). When I start the car, the lights go away and the car is able to run fine, but the lights return when the car is turned off and eventually the alarm comes back). I was able to get the issue to stop both times by locking and unlocking the car via the manual key vs remote.

However, during the 3rd most recent instance using my manual key hasn't worked, and now the car won't start. I should note that after the first instance, the low tire pressure warning has been on in the car despite the tire pressure being checked both at home and via dealership and noted as having optimal pressure.

After doing some research as well as watching your youtube video, I believe there's an issue with the car's computer and that a hard reset might be the solution, but I wanted to first get your advice and input. I believe there's possibly a bug in the computer that is causing the car to believe it has issues it doesn't.

Any advice or insights would be greatly appreciated!
Jun 16, 2026 at 8:45 PM
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APPLESTOANNIE
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I should also note, it's a keyless, push-to-start engine, and that there were no issues with the car until I went out of town for 2.5 weeks and the battery died from being idle. I purchased and installed a replacement battery from AutoZone, and a month later is when these issues started.

After the second occurrence, I replaced the battery again to be safe, but found it was def a systems issue vs a problem with the battery.
Jun 16, 2026 at 9:22 PM
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STEVE W.
  • ASE Certified Mechanic
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A common reason for this is a bad door or hood switch that sets the alarm off. You can see the trigger switches in the second image in the diagrams. The problem is that you would need to test each of the 6 switches in turn and see if the alarm still goes off after each one is bypassed, or find someone with a scan tool who can look at the body and alarm modules and see what is triggering it and then repair the problem. There will be a notation in there saying something like "alarm triggered by left rear door switch". The hood switch is a common one and as your problems started after a battery change I'd look at it first before going for a scanner. The switch is part of the front hood latch assembly. It has a 2 pin connector, to test it you unplug it and put a piece of wire across the two pins so it thinks the hood is closed all the time. Or adjust the latch up a small amount so the hood presses it down harder. Then see if the issue goes away.
Jun 18, 2026 at 2:46 AM
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