I want to get a second pcm (maybe from a wreck yard) for my car to play with. I have an 03 ssei and was wondering if each model year is different. For example can I use an 00-02 pcm and plug it in or do I need to reflash first with hp tuner.

With A 00-03 PCM you should be good as far as I know ,
you might be able to use as far back as 97 not shure
If Im wrong some one will correct me.

something tells me that you need a PCM from the same year.....

i think as long as he has a 00-05 it will be fine.. however the theftlock in the radio might lock on you if you have the wrong VIN PCM in the car.

Oh yeah I forgot to say that youll probally have to do the security learn on your new PCM when you switch before it will start