Honda released the 2004 Civic during the 2004 model year. Since Honda had not yet released the Civic SI, there was only one Civic model manufactured during that year. Similar to nearly every other car released in 2004, the Honda Civic featured incandescent headlight bulbs housed in a reflector assembly that magnified the light emanating from the bulbs. These can be easily changed in case they burn out.
Use a 10-mm socket to loosen the bolt holding the battery in place, if it is in the way. Once the bolt is loose, you can slide the battery far back enough to reach the headlight assembly.
Locate the electrical wires feeding into the headlight assembly. Press down on the plastic tab that the wires connect to and turn the retaining ring 1/4 turn counter-clockwise. If you have trouble moving it, insert the blade of a flat blade screwdriver into the tab to press it down. Remove the bulb from the headlight assembly.
Slide down the retaining wire holding the bulb in place to release the bulb. The bulb in each of the two Honda Civic headlight assemblies has a thin retaining wire--be careful not to press too hard, as the wire can break easily.
Insert a new bulb and slide the retaining wire up. Place the bulb into the headlight assembly and turn the tab 1/4 turn clockwise.
Slide the battery back into place. Tighten the bolt to secure the battery to the vehicle.
Wear gloves when completing this task. Since you will be working in a small area, gloves can save your knuckles some wear and tear.
Never touch the glass on the new headlight bulb. Skin oils left on the glass will cause the bulb to fail quickly.