Folks can look at as 'recommendations' too, but note that when my stuff came
back and found that the owner didn't follow my manual/specifications/etc...I'd
not sign off on any warranty the service department sent back to my design teams
Warranty, but okay, take as a recommendation from the OEM...so if you don't follow
that recommendation...then why would the OEM provide warranty?
My industry sector was not automotive, but no different from any market
sector.
It is my design, my specification that cost me tons of money to design
to a specification...and pay for certification by the regulatory agencies
and then field the product.
All that costs me money and expect to make money to stay in business.
Part of that business are warranty costs, plus other overhead expenses
As for the 'read me first', 'manual', etc documentation...it is well
established in the courts that folks generally do NOT read them. OEMs
can NOT force them to read them, nor follow them...so the courts just
look at 'good faith' that all that stuff is in the product...so if
you toss them all without reading them, or understanding them...is is
okay with the courts and you will not get warranty/liability/etc