Types of Parts Damage
Each time you race you will have some sort of parts damage. The three types of damage in EV3 are engine damage, drivetrain damage, and tire damage.
Engine damage happens when you hit the rev limiter on the car. The amount of damage depends on how long you hit the rev limiter and what parts are installed. Drivetrain damage happens when you have too much torque and the axles, driveshaft, differential, and transmission. Drivetrain damage is different from engine and tire damage because engine and tire damage happens gradually. Drivetrain parts are either broken or they're not. Tire damage happens from spinning the tires. Burnouts will cause a small amount of tire damage each run but you can have more damage from spinning the tires when you launch as well.
Repairing Parts Damage
Parts damage can be repaired at any time. If you go to the garage, the damage for your selected car will display directly under the graph on the left hand side. Prior to each race you will also see a repair screen that gives you the option to repair or not. The repair screen will show you three different ways to repair the damage. The first option is to pay points and wait the specified amount of time (if any wait time exists) for the damage to be repaired. The second option is to pay the points but also pay one coin in order to instantly repair damage without waiting. The third option is to pay with only coins and also results in instantly fixing all damage without waiting.
Points are earned by racing in career mode, and coins can be bought by clicking the green plus "+" sign in the top right of the game.