I just replaced the plugs in my 2003 HCH, and I noticed when I was cleaning up that there were two different types installed originally. I replaced with 8 Denso Iridium plugs. I removed 4 Denso and 4 NGK plugs.

BTW - what a pleasure replacing those plugs. It was the easist I have every done I have replaced plugs on LOTS of cars (american and imports). The HCH is far easier than any other car I have ever worked on.

 

I had the same experience with our '06 Civic Hybrid: front "row" were NGK, and back row were Denso, ie: one of each brand per cylinder. I was not replacing, just taking a look, around 65,000km.

 

I saw this old post and felt the need to respond. I bought a 2008 Honda Civic Hybrid about 3.5 yrs ago from a friend who had all service records. She has plugs changed by dealer service when recommended, I think at 60k. I bought it at about 98k and saw mpg go down to 28 -30, so changed plugs at about 112k. MPG improved to about 38 - 41k. Anyway found same issue with different set of plugs in back than front NGK & Denso as prior post. My thought is that it was laziness of service tech. Too much time to change the back and they knew prior owner wouldn't question or want to see replaced parts. Techs only get paid a certain amount for jobs that are based on a time scale, i.e. they get paid maybe 30 min to do a job but the job may take longer that they don't get paid if they go over so they take shortcuts whenever they can
My brother is a mechanic and worked at a dealer shop in the past and he said that is likely to happen
I apologize for the long post.

 

FWIW, same thing on one of my '06 HCH2. Denso rear, NGK front. Both were the correct versions of plugs. ALL were in need of replacement and looked equally sh1tty. I would not conclude that it was laziness, and I would conclude that they had all been previously replaced at the same time.

The rears aren't that hard to do. The one on the driver's side end is a little tricky, but There's nothing special about getting the job done. If you take 2 minutes to pull the compartment cowl, it makes replacing the rear plugs an absolute breeze.

It's very irregular to have two spark plugs per cylinder. If it's not done by a dealer, I wouldn't be surprised if someone didn't realize there was another set in the rear.