Take it to a mechanic to have it checked. It's most likely to be related to the cars' electronics.

My suspicion is that it is a ploy to squeeze a few more bucks out of you, that's usually the case with these sorts of additional   service recommendations. If you doubt the dealer's advice ask for proof that the service is needed.

It's important here to understand that it is not Nissan advising you have the injectors serviced, it's the dealer. I would be inclined to reject the advice, but if you are concerned about it have the dealer justify the recommendation. Ask to see the damaged parts, get a written report etc.