Za Longman Contemporary (Online)
warranty- a written agreement in which a company selling something promises to repair it if it breaks within a particular period of time
guarantee:
[1] a formal written promise to repair or replace a product if it breaks within a specific period of time [= warranty]
ex> They offer a two-year guarantee on all their electrical goods
[2] a formal promise that something will be done
ex> I'm afraid there's no guarantee of success.
[3] a) a promise that you will pay back money that someone else has used or borrowed, if they do not pay it themselves
b) something valuable that you give to someone to keep until you have done something you promised to do
ex> The bank is holding the airline's assets as guarantees.