Abstract: A system to and method of monitoring a condition of a process tool. The system monitors a condition of a process tool to correctly detect a faulty operation or malfunction of the process tool. The system to monitor the condition of the process tool includes a first model storage unit to store one or more good models generated by data associated with the process tool, a second model storage unit to store one or more faulty models generated by the data associated with the process tool, a model selector to receive tool data from the process tool, and to select one of the good models and one of the faulty models in association with the received tool data, and an error detector to receive process data from the process tool, to compare the received process data with the good and faulty models selected by the model selector, and to estimate a condition of the process tool.