Five Whys
• Goal of applying the 5 Whys method is to
determine a root cause of a defect or problem
• It is a critical component of problem solving
training delivered as part of the induction into the
Toyota Production System
• Use caution when using this approach for
anything other than a simple mechanical failure.
• Tab 1 page 8
54
Five Whys (2)
Use caution when using this approach for anything other than a simple
mechanical failure. Reasons for this advice include:
• Tendency for investigators to stop at symptoms rather than going on
to lower level root causes.
• Inability to go beyond the investigator's current knowledge - can't
find causes that they don't already know
• Lack of support to help the investigator to ask the right "why"
questions.
• Results aren't repeatable - different people using 5 Whys come up
with different causes for the same problem.
• Tendency for vertical dives and very little lateral analysis
55
5 Why Analysis: The Failed Pump
Pump
Stops
Pump
Testing
Are we there yet?
Failed
Bearing
Temperature
Alarm
Bypassed
Inadequate
Lubrication
Reservoir
Anomaly
Not Noticed
Reservoir
Not
Filled
Sight Glass
Issue
Not Noticed
Sight Glass
Installed
Upside Down
Sight Glass
Not
Anti-Murphied
Drawing Not
in Work
Package
"Real Nukes
Don't Need
Drawings"
Correct Configuration
Document
Control
Backlog
Recent
Downsizing
©
2014, William R. Corcoran, NSRC Corp.
© 2014 W. R. Corcoran
56
Five Whys: Discussion
©2014 JPDrago MetalTek RCE Workshop