Ionic, Angular - ChangeDetectorRef is undefined

 hardResetCallback = (car:Car) => {
    this.car=car;
    this.ref.detectChanges();
  }

Use fat arrow function to prevent creation of “this” inside the scope of your hardResetCallback method.

See more about arrow functions here.

Relevant quote:

"In classic function expressions, the this keyword is bound to different values based on the context in which it is called. With arrow functions however, this is lexically bound. It means that it uses this from the code that contains the arrow function."