The 5 Why method (5 Whys) is a simple yet powerful technique for identifying the root cause of a problem. Developed by Sakichi Toyoda, founder of Toyota Industries, this method consists of asking the question “Why?” repeatedly, generally five times, to dig ever deeper into a problem’s chain of causality until reaching its fundamental source.
Steps for applying the 5 Why method:
- Identify the problem: Clearly define the problem you are seeking to solve. Make sure that every member of the team fully understands the initial situation.
- Form a team: Bring together a team of people with diverse knowledge of the process or the problem. Their collective perspective is essential for a thorough analysis.
- Ask the first “Why?”: Ask why the problem occurred. Note down the answer. This first answer is often a visible symptom of the problem, but rarely the root cause.
- Ask successive “Whys?”: For each answer obtained, ask “Why?” again. Repeat this step until you have asked the question five times or until the team has identified the root cause of the problem. It is important not to jump to conclusions too quickly and to ensure that each answer is based on facts and concrete data.
- Analyse the answers: At each step, check the logic of the answers and make sure that the causes identified are directly linked to the initial problem.
- Determine corrective actions: Once the root cause has been identified, discuss possible corrective actions to resolve the problem definitively. Make sure these actions are specific, measurable, achievable, realistic and time-bound (SMART).
Example of the 5 Why method:
- Problem: The machine stopped.
- Why? The machine blew a fuse due to an overload.
- Why? There was an overload because a bearing was insufficiently lubricated.
- Why? The bearing was not sufficiently lubricated because the lubrication pump was not working properly.
- Why? The lubrication pump was not working properly because its filter was clogged with impurities.
- Why? The filter was clogged with impurities because it had not been changed according to the recommended maintenance schedule.
- Why? The lubrication pump was not working properly because its filter was clogged with impurities.
- Why? The bearing was not sufficiently lubricated because the lubrication pump was not working properly.
- Why? There was an overload because a bearing was insufficiently lubricated.
- Why? The machine blew a fuse due to an overload.
Result: The root cause of the problem is the failure to follow the maintenance schedule. The corrective action could be to strengthen preventive maintenance protocols and staff training on the importance of regular maintenance.
Advantages of the 5 Why method:
- Simplicity: The method requires no sophisticated tools or in-depth training, which makes it accessible to everyone.
- Effectiveness: It enables the root cause of problems to be identified quickly and avoids focusing solely on the symptoms.
- Collaboration: It encourages communication and collaboration within the team, thereby strengthening members’ commitment to finding a lasting solution.
- Precision: It makes it possible to go beyond appearances and uncover the underlying causes, which leads to more effective solutions.
In conclusion, the 5 Why method is an essential Lean Management tool for problem solving. It breaks complex problems down into fundamental causes and enables effective corrective actions to be put in place, thereby improving processes and the quality of products or services.
Xavier Schuster
Consultant at SXE Consulting. Industrial consulting firm based in Luxembourg, 25 years of experience in operational excellence.
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