5 Whys
The 5 Whys (5Y) is an iterative root cause analysis technique developed at Toyota that identifies the underlying cause of a failure by repeatedly asking 'why' five times to trace the cause-and-effect chain from the observable symptom to the fundamental defect. It is used to uncover actionable root causes for preventing recurrence.
In CMMS/Shop Floor maintenance contexts, the 5 Whys is applied by starting with a specific work order failure mode, such as 'Bearing seized,' and documenting the answer chain: 1st Why identifies the immediate failure mode; 2nd Why reveals the technical cause, like lack of lubrication; 3rd Why uncovers a system or process gap, such as a missed PM task; and the 4th and 5th Whys pinpoint an actionable root cause, like undefined PM frequency or missing training. This root cause is then used to update maintenance protocols or asset reliability strategies to prevent recurrence, ensuring continuous improvement in equipment reliability and reducing unplanned downtime.
When should 5 Whys be used over FMEA or Fault Tree Analysis?
Use 5 Whys for specific, repeatable failures or unexpected downtime where the cause is unclear but the path is linear; use FMEA/Fault Tree for complex, multi-variable systems or prospective risk assessment.
What is the 'Three-Legged 5 Why'?
An advanced variation that questions three lines: Occurrence (Technical/Mechanical), Detection (Quality/Sensor), and Systemic (Process/Policy) to uncover hidden weaknesses in knowledge management or maintenance protocols.
How is 5 Whys integrated into CMMS?
The final root cause and corrective action are logged in the failure report module, triggering updates to preventive maintenance (PM) schedules, SOPs, or training records to close the reliability gap.