Root cause analysis (D4)

In D4, the team looks for two things: what produced the defect, and what failed to stop it before it reached the customer. Kanriq handles them in two separate trees.

The two 5 Whys trees

• Occurrence tree — why the defect occurred: process, tooling, settings, material, method, and the rule that governs them.
• Non-detection tree — why the controls did not stop it: what they check, their method, their frequency, and why they were designed or maintained that way.

Each level answers “why” to the one above, down to a cause the team can act on.

1. Click Propose tree (AI) under the tree you want.
2. Review the cards: a sourced card cites the passage of the case file that supports it; a card marked interpretation goes beyond the file and must be checked.
3. Edit a card directly, add a level with +, or split a path into two causes.
4. Accept the proposal: nothing is saved before that.
5. Answer the verification question — which action validated the cause? (ideally, reproducing the defect) — then click Validate root cause.

Supporting tools

Tool	What it is for
Ishikawa (6M)	Sort possible causes into Manpower, Method, Machine, Material, Measurement, Environment (Milieu).
Timeline	Put dated events back in order, from your own words or the facts in the file.
Is / Is Not	Pin down the problem on five dimensions: part, operation, machine, period, defect.

Note

In the Is / Is Not table, a cell the case file cannot establish reads “To check: …” followed by the item to verify — a question for the team, never a statement.

Supporting tools are validated separately and never block closure: only the 5 Whys determines whether D4 can be closed.