Mock a method call that is in the same class i'm testing, is it really code smell?

I'm trying to test a service class (responsible for calling the repository layer and do some operations if needed), basically, this is the class I'm trying to test

class CarServiceImpl{
  public Car findById(String id){
      //call repository layer to find a car
  }

  public void deleteById(String id){
      Car car = this.findById(id);
      if(car != null){ 
          //Call repository layer to update the car
      }else{
          Throw NotFOundException();
      }
  }
}

As you can see I call the findById method on the deleteById method, so my questions are.

1. is it really code smell to call a method on the same class? I don think I should create a separate class to find a car by id.

2. how can I mock the call to "findById" on the "deleteById" method, if I use Mockito.when(carServiceImpl.findById("car1")).thenReturn(carModel); it stills call the method so i'll need to mock the call to respository for finding by id too, even when i already tested the method findById.