Dear Sanjeev I will give an answer which is somewhat generic as compared to Mani Kumar's. 1. In case of a new order and you are not sure of meeting customer requirements, Please do an FMEA even if the process exists. 2. in case you receive sporadic complaints and your records show that the system is in place, please do PFMEA. 3. In case of a reengineered/improved process as a result of six sigma or any other method carryout a PFMEA. Please remember PFMEA is the only proactive tool. so, you need to get people use it more and more. you may refer to AIAG publication but modify severity and probablity ratings in case you are from a different industry.