Defect:-
Defect means imperfection; shortcoming; something lacking in completeness or perfection. While in fault there is an element of blame,the word defect has no such implication directly.

Example of Defect:
“There are several defects in our system of education”

Examples of fault:
She loves me inspite of all my faults.

Her only fault is excessive shyness.

There is a fault in the electrical connections.

To find fault with means to complain about:

I have no fault to find with your work.

To a fault means excessively: she is generous to a fault.

At fault means in the wrong, at a loss; in a puzzled state:
My memory was at fault.

Fault (in singular form only)means also responsibility for being wrong:

Whose fault is that we are late?

It is your own fault.

The fault lies with you, not with me,you are to blame.