In law, a presumption means the burden shifts from the plaintiff to the defendant.  Here, that means the court will require the defendant to disprove a car is a lemon if the plaintiff establishes the presumption. In California, the courts will presume a car is a lemon if the following additional facts occur and a car is still not fixed: four repair attempts and still not fixed; Two repair attempts for a serious problem that can cause serious injury or death and it is not fixed; 30 day in the shop for a problem covered by warranty. As you can see this presumption relates to the “reasonable number” of repair attempts in the legal test for a lemon.  The presumption means the courts have decided what they believe is a reasonable number of repair attempts in specific situations.