The Nissan manual or the Nissan's manual?

Question

I would like to know which of the following sentences is correct and if possible, a source accompanying your answer. (Note: Only choose which sentence is correct as regards to the title, do not mind any mistakes you might find in the sentence.)

The Nissan manual is there to help you with any trouble you might have.

OR

The Nissan's manual is there to help you with any trouble you might have.

I do not think there is any difference, but preferably the answer follows British English rules.

Also, there is no specific Nissan, it is just in general.

Answer 1

If "Nissan" is referring to the company, the proper phrase is "The Nissan manual" as "Nissan" here is being used to modify "manual" (Which manual? The Nissan manual.). "The Nissan's manual" suggests that it is a manual belonging to "The Nissan"—that is, a manual for a specific car.

Answer 2

Presumably this is a manual for one particular model, and not a general manual issued by Nissan. Provided it is the former, then it will be very specific, not only to the model but perhaps a particular batch of that model. So it seems to me 'The Nissan manual' is not a very good way of describing the book in question.

How I described it would depend on to whom I was talking. If it was a prospective buyer I might say 'the car's manual'.

If it was to a neighbour, to whom I was talking about car manuals in general, because we had been discussing a problem he was having with his, I might say 'In the Nissan's manual it says....'.

If it was to the Nissan Service Department, I would refer to the exact model number 'In the XYZ manual it says the car runs on water'.

etc.