My factory alarm failed to arm after pressing lock on my key fob and I suspected a bad actuator. The alarm will not arm if all the doors and the trunk are not locked. I had replaced both door actuators already with OEM ones so have encountered this previously. Checking all of my locks, the trunk was not locking.
Found this guide here for replacing the trunk actuator. Confirming the part number 74896-S6M-A01 online, I found an aftermarket for $13 USD on ebay, Dorman 746-747 for $70 USD on Amazon and an OEM for $130 USD. Ordered the cheap aftermarket one since I don’t intend to keep the car for long. OEM pricing is pretty ridiculous for a molded part with just a small electric motor and some gears.
In the meantime to lock the car, there is an access panel in the hatch for replacing the third brake light bulb. There is a white lever accessible which can be switched to lock the trunk. If it is unlocked, you can switch it to the locked position before closing the trunk. If you can’t unlock it with the remote, you can crawl through the trunk to unlock it.
Will update once I install it and see how long it lasts.