▲guarantee (《剑桥高级学习词典》)
a promise that something will be done or will happen, especially a written promise by a company to repair or change a product that develops a fault within a particular period of time.
The shop said they would replace the television as it was still under guarantee.(《剑桥高级学习词典》)
▲warranty (《剑桥高级学习词典》)
a written promise from a company to repair or replace a product that develops a fault within a fixed period of time, or to do a piece of work again if it is not satisfactory.
The car is still under warranty. (《朗文当代》)
▲从以上可以看出,guarantee 与 warranty作“保修;保修证书”解时是同义词,under guarantee 与 under warranty 也均表示“在保修期内”。