What is the 5-Why Analysis Method?
5-Why Analysis is a fundamental quality management tool for Root Cause Analysis (RCA). The method consists of repeatedly asking the question "Why?" to drill down into the previous answer. The goal is not to find human error, but to uncover hidden process or system failures. The rule of "five" is just a guideline – sometimes three iterations are enough to find the actual root cause, other times it takes seven.
When and why should you use 5-Why Analysis?
- Customer Claims (8D Report): A standard requirement for developing steps D4 (root cause analysis) and D6 (corrective actions).
- Automotive Standards: The tool is fully compatible with and required by IATF 16949, VDA methodologies, and ISO 9001.
- Process Improvement (Lean Management): Quick identification of waste (Muda) and process failures.
What is a 3-Legged 5-Why Analysis?
Modern manufacturers and OEMs require an advanced form of this method. The problem is not broken down in just one path; root causes are investigated in 3 independent directions simultaneously:
| Leg | Question Goal | Root Cause Example |
|---|---|---|
| 1. Occurrence | Why did the error physically occur during production? | Excessively worn tooling. |
| 2. Detection | Why did the inspection fail to catch the defect before shipping? | Camera sensor out of tolerance. |
| 3. System | Why did our QMS allow this situation to occur? | Error in the PFMEA process, missing TPM maintenance. |