Gas door latch not working

How about a key ?

Luggage Compartment Description and Operation (Sedan)
Rear Compartment Lid Release
The rear compartment lid can be released in one of three ways:
• Inserting the key into the key lock cylinder, if equipped
• Operating the rear compartment lid release switch
• Using the keyless entry fob
To operate rear compartment lid with the rear compartment lid release switch or with the rear compartment release button on the key fob, the gear selector may be in any position, but vehicle speed must equal 0 for the rear compartment lid to release.
When the rear compartment lid release switch is pushed, the rear compartment lid release signal circuit to the body control module (BCM) is grounded. BCM then grounds the coil side of the trunk release relay through the trunk release relay control circuit. With this voltage is applied to the rear compartment lid release actuator, opening the rear compartment.

do you know how to do electrical testing ?

Circuit/System Verification
Ignition ON, observe the scan tool Trunk Release Switch parameter while pressing and releasing the rear compartment lid release switch. The parameter should change between Active and Inactive.
? If the parameter does not change, refer to Trunk Release Switch Malfunction.
Command the trunk release with a scan tool, the rear compartment lid latch should release the trunk lid.
? If the rear compartment lid latch does not release, refer to Rear Compartment Lid Latch Malfunction

You may want to take it to a repair shop .

If the gas( or any gauge) is low or maybe an exterior light out. There will be a light on in the dash. The beep is there to remind you to look at the dash. Could be door open,trunk, hood, gas lid.. could be some engineer just did it to annoy us.

emergency release should be in the trunk as for the closing of the trunk, you need to disconnect the cable at the trunk latch until you can get it fixed

There should be manual release cable inside the trunk behind the trim panel near the gas door location.

Open trunk and pull cable in left rear side trunk panel. This is an emergency release for the fuel door. You may have to pull gently out on fuel door while tugging at release cable several times. When the door opens oil latch solenoid tip and bend tab on door latch about 2mm towards hinge.
The fuel door is flimsy and tends to get bent. Once it is bent it prevents the latch solenoid tip from releasing the door latch.

You can get to the latch through the trunk. In the trunk, pull the liner away from the area adjacent to the fuel door. You'll see a black cable that goes to the fuel door latch behind a metal frame. Reach in and turn the latch mount 90 degrees to release it from the fuel door frame. Your fuel door will now be open. You will need to repair or replace the cable, but at least you'll be able to fuel up for now.

You can get to the latch through the trunk. In the trunk, pull theliner away from the area adjacent to the fuel door. You'll see a blackcable that goes to the fuel door latch behind a metal frame. Reach inand turn the latch mount 90 degrees to release it from the fuel doorframe. Your fuel door will now be open.

For a fix, look at this low cost solution: http://www.instructables.com/id/Fix-Broken-Fuel-Door-Cable-on-Honda-Civic-82170/

I tried it over the weekend. It works great.

The cable hooks up to the latch under your left foot and goes back to the latch on the gas fill door. I believe you can take the trim loose from the trunk to see what the cable is doing. May have snapped or something on the latch near the fuel door broke. You should be able to manually open the door.

Its not in the trunk,Its either in the glove box or on the floor left side of drivers seat

trunk latch cable probably needs to be replaced