DIY, change the ignition coils on your Nissan Altima 2.5L, produced in the year 2003. To make the repair you will need four new spark plugs, a 10 mm socket wrench, a ratchet with a 5 mm Allen bit and a spark plug socket. It is the kind of a repair that you can do it by yourself in about 30 minutes.
First of all, you have to open the hood of your car and unplug the negative cable of the battery to avoid electrical problems. Then go to the engine and remove the engine cover. It is held by four 5 mm Allen bolts (shown in the image below) that you can unscrew using a ratchet with a 5 mm Allen bit or an Allen wrench.
Lift off the cover and gain access to the four ignition coils. Unscrew the 10 mm bolts that secure them, using the socket wrench and disconnect their electrical harnesses, all marked in the picture below. You can do the last task by pressing the safety tabs with your fingers, or using a flat blade screwdriver.
At this point, you can use the spark plug socket to remove the four spark plugs. After you do it, install the replacements carefully. Then insert the coils back into their sockets, secure them with the 10 mm bolts and plug back their harnesses. In the end, install back the engine cover and reconnect the negative cable on the battery and that’s it. This is all you need to know, if you wish to change the spark plugs on your Nissan Altima 2.5L, manufactured in the year 2003.