This paper proposes methods to drastically reduce the expensive analog fault simulation currently used to create cell-aware fault models. By exploiting low-power properties of common CMOS designs, most defects in the transistor-level netlist containing parasitics can be represented by just two canonical fault classes. Via simple circuit analysis, we show that faulty behaviors are completely predictable as the defect resistance parameter value varies from zero to infinity, thus eliminating the need for circuit simulation at multiple parameter values. The two canonical fault classes can be modeled by transistor switch stuck-open and stuck-closed faults. Rather than enumerating the full combination cell input patterns to search for defect detection conditions by analog fault simulation, switch-level test generation can obtain those input conditions directly, thereby reducing significantly the role of analog simulation to that of ranking conditions in terms of detection effectiveness.