Lean manufacturing originated from the Toyota Production System in 1990, widely known as a crucial principle in the manufacturing process to enhance performance. The essential policy of lean thinking is to reduce waste in every aspect of the production system. Hence, the waste identifier model plays a significant role in waste reduction activity. This paper proposes a questionnaire-based model for assessing waste in an Engineering to Order (ETO) environment which has no historical or statistical data due to the low-volume and high-variety products. This paper presents an adaptation of the Failure Mode and Effect Analysis method to analyze wastes and define priorities for actions aimed at minimizing the lean wastes based on the criteria of severity, occurrence, and detection (SOD). This study not only adapts the previous SOD table but also modifies the table based on the ETO characteristics. A Pareto chart is applied to rank the waste that needed to be prioritized. A case study was conducted to validate the assessment model. Concluded from the pilot study, the assessment results do match with the management’s opinion. Before obtaining alternative solutions to reduce waste, the author worked together with the company’s management team to analyze the root cause of each waste that has a high Waste Priority Number (WPN).