This procedure will work on both the 2002-2006 Altima and Sentra 2.5 l4 motors.
Tools:
5mm Allen
10mm socket
This is a very easy procedure, and can be done by anyone with a basic mechanic background.
1. Using the 5mm Allen wrench, remove the plastic engine cover bolts, and remove the engine cover.
2. Using the 10mm socket, remove the bolt holding the ignition coil on, and simply remove the ignition coil. Be careful removing the electrical clip, as these can be brittle over time. Carefully wiggle the clip off instead of tugging on it.
For these models, also be sure to check the main ground cable. This cable goes from the negative post on the battery to the transmission, and can corrode and break over time and with engine movement. This is the main ground to check. If it appears corroded or damaged in any way, it must be replaced before proceeding to do any other electrical work on the car.