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For new car buyers, both leasing and financing have unique advantages and disadvantages. Leasing comes with lower monthly payments, but you don’t build ownership and are usually restricted from fully customizing or selling the car. With financing, you will own the car once the loan is paid off. You can also sell it whenever you want if you settle the balance, but modifying a financed car depends on the finance agreement itself.

Most agreements don’t come with customization stipulations – always check it before wrenching — but minor modifications that can be reverted to stock shouldn’t pose any issues as long as they don’t affect the car’s value long-term. Major modifications that permanently change the car and can affect its value or safety are usually a different story.

Although these still aren’t necessarily prohibited, the lender has a legal interest in the car. This means that if the value of the car is compromised, it could mean a breach of agreement on your end. Always make sure to check the fine print and ask the lender/dealership for consent before doing any mods to your vehicle.

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Since there are different types of loan agreements, there are also different rules to follow. For a traditional unsecured personal loan, you own the car immediately. This means that the lender has no claim on the vehicle and cannot repossess it if you stop paying. That typically allows you to modify a car to your heart’s content. Auto loans or secured loans are different since the lender holds a lien until the loan itself is fully paid off.

This can limit the type of modifications you can do since the lender now has a claim on the vehicle, and is more likely to care if the car’s value has been affected. For instance, some auto loans will explicitly state that the car needs to be kept in its original condition and should not have anything done to it that would void its warranty in order to preserve its value. So, if you do a permanent modification and manage to void the warranty, it could mean a breach of the agreement.

The idea is simple: the lender wants to preserve a car’s value as much as possible during the agreement. If some of the modifications you make affect the resale value negatively, and you owe more than your car’s resale value, you will have to pay to bridge that gap when settling the loan. This is why it’s always best to talk to your lender and check the agreement, as that is the only dependable way of knowing whether you can modify your car at all.

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The idea is to modify a car so it can be easily reverted back to stock without voiding warranties. The good thing is that the Magnuson-Moss Warranty Act (via Congress) prevents automakers from automatically voiding your warranty simply because you modified the car unless the modification has caused damage. Upgrades such as wheels, tires, tints, seat covers, or floor mats should be safe because they can be easily reverted to stock.

Performance mods, including slip-on or bolt-on add-ons, are also less likely to get you in trouble compared to those that require cutting, welding, or permanently altering the vehicle’s core systems. Some mods, even if they are fine with your finance company, can be illegal. For example, a simple, slip-on exhaust muffler that can easily be reverted to stock might be okay with your lender, but this is one of the few popular mods that are illegal in California. 

Lastly, always make sure to keep the removed original parts if you do decide to modify, especially software logs for any potential ECU tunes or similar. This will allow you to fully revert your vehicle to stock form when it comes time to sell the vehicle or return it at the end of a finance agreement. There is no one-size-fits-all solution, as everything depends on your specific agreement and the mods you want to do.