A factory warranty is a contract between you and the car’s manufacturer. An extended auto warranty is a contract between you and the warranty company. They both promise to take care of any covered repairs, provided that you follow certain expectations set by the manufacturer or warranty administrator. But like any contract, it can be broken if you don't hold up your end of the bargain, so it is important to know what circumstances can void your warranty.
Salvage title: If your car was in a major accident and was deemed a total loss or given a salvage title, your entire warranty is voided. When buying a car from a private seller or an independent car lot, keep this in mind. For extra assurance, you can purchase a vehicle history report. It will tell you if the vehicle has a salvaged title or not.
Misuse of the vehicle: This is a broad term. It often includes racing or competition of any type, overloading the vehicle, or off-road. Basically, anything that is outside of normal use can be considered abuse or misuse. There are automakers that will void your entire warranty if there are signs of misuse and this decision is typically left to the discretion of the warranty administrator.
Environmental damage: If mother nature rears her head and your vehicle was damaged in a fire, flood, earthquake or any other environmental disaster, the automaker or warranty administrator will not honor your warranty.
Altered odometer: If your car's odometer has been tampered with, damaged, or replaced then it is usually grounds for the manufacturer or warranty administrator to void your warranty. There's no surefire way to know if your odometer has been tampered with, but you can order a vehicle history report which will check for inconsistencies in mileage reporting.
Neglect: Failing to do routine car maintenance on your vehicle is considered neglect by most manufacturers. If a part should fail due to the fact that the car has not been maintained properly then the manufacturer or warranty administrator is not responsible for the repair cost.
Use of dirty or improper fluids: If your car calls for gasoline and you accidentally use diesel fuel, any damage that occurs will not be paid for by your warranty. This goes for fluids that are dirty or the use of improper fluids for a particular part of your vehicle. Alway make sure that you are using the fluids that are recommended by your manufacturer. If you are unsure of what fluids to use, consult your owner’s manual.
Aftermarket parts or modifications: In order for an aftermarket part to void your warranty, the dealership must prove that the part caused the needed repairs. HOwever, if the cause of failure is unclear, the dealership will charge you a diagnosis fee. If the aftermarket part is found to have caused the failure, then the dealer can void your warranty. If the aftermarket part did not cause the failure, the dealership will refund your the diagnostic fee.