When the class of the object on which Equals(object) is called does not define its own Equals(object) method, an Equals(object) method defined in one of its base classes will be called instead. In the worst case, the Equals(object) method of System.Object will be called, resulting in a reference equality check. This is probably not what was intended.

Classes that implement the == operator should also override the Equals(object) method, because otherwise the two forms of equality will behave differently, leading to unexpected behavior.

Implement an Equals(object) method for the highlighted class. Examine subclasses of the class highlighted to determine if they should implement their own equals method too.

The output of this example states that "car1 does equal car2" despite the fact that one is a leaded version and one is an unleaded version. This is because the GasolineCar class is inheriting Equals(object) from Car and that method states that two Cars are equal if their make and model are the same.

In the revised example, GasolineCar overrides Equals(object), and the output is "car1 does not equal car2", as expected.

Microsoft: Equality Operators, Equality Comparisons (C# Programming Guide).