After checking out a local Toyota dealership for a spark plug replacement service for my 2009 Prius, I was dismayed to find that they were going to charge around $250! I did a little research and found that with some basic tools and tutorial videos on YouTube, I can install this myself in under an hour. I'm moderately mechanically savvy so I decided to give it a try and was able to change all four spark plugs in the space of an hour. A few tips for installation in a 2004-2009 Toyota Prius (Gen 2): Remove any debris and clean the top. engine, particularly near spark plug wells; This prevents dirt from entering the cylinder. I used a 6" extension for my socket wrench to access the plugs without too much trouble. The plug furthest from the driver is the most difficult to remove; Disconnecting the wiring harness may help. Aside from doing something new, it was comparable to an oil change or easier (less messy of course). As of January 15, 2016 these spark plugs are working great!