GUIDE6 min read · March 12, 2026
5 Why Analysis: 6 Real Examples From the Shop Floor
The 5 Why technique sounds simple but most teams stop too early or ask the wrong questions. Here are 6 real manufacturing examples that show you exactly how deep to dig.
Why most 5 Why analysis fails
The 5 Why technique was developed by Sakichi Toyoda and is the cornerstone of the Toyota Production System. It is deceptively simple: when a problem occurs, ask "why?" five times to get to the root cause instead of the symptom.
In practice, most teams stop at Why 2 or Why 3 — the point where the answer is uncomfortable, politically sensitive, or points to a systemic failure rather than a single person's mistake. The result is a corrective action that treats the symptom and the problem returns within weeks.
A properly completed 5 Why will almost always point to one of three systemic root causes: a missing standard, a standard that isn't followed, or a standard that isn't visible at the point of use.
6 real examples
EXAMPLE 1
Problem: A customer received 24 defective parts in a shipment
W1
Why? → The parts passed final inspection but had a burr on the mating face
W2
Why? → The inspection checklist did not include a check for burrs on that face
W3
Why? → The checklist was written before the new tooling was installed 6 months ago
W4
Why? → There is no process to update inspection checklists when tooling changes
W5
Why? → Engineering change orders do not trigger a mandatory quality document review
ROOT CAUSE
The engineering change order process has no requirement to update quality inspection documents.
CORRECTIVE ACTION
Add a mandatory "Quality Document Review" step to all engineering change orders, with sign-off from the quality manager before changes go live.
EXAMPLE 2
Problem: Machine downtime on Line 3 increased 40% last month
W1
Why? → The hydraulic press on Line 3 is breaking down 3× more often than normal
W2
Why? → The hydraulic fluid is contaminated with metal particles
W3
Why? → The filter replacement schedule is 90 days but the filter is clogged at 45 days
W4
Why? → The filter interval was set 8 years ago for a different duty cycle
W5
Why? → There is no process to review PM intervals when production volumes change
ROOT CAUSE
Preventive maintenance intervals are set once and never reviewed, even when machine duty cycles change significantly.
CORRECTIVE ACTION
Conduct a full PM interval review for all critical equipment. Link PM schedules to production volume triggers so intervals adjust automatically when throughput changes by more than 20%.
EXAMPLE 3
Problem: Order picking errors are running at 3.2% — target is 0.5%
W1
Why? → Pickers are selecting the wrong SKU from the bin
W2
Why? → Bins for two similar SKUs (A4412 and A4421) are adjacent and look identical
W3
Why? → The bin labels are small and the part numbers differ by only 2 digits
W4
Why? → The warehouse was laid out alphabetically by SKU number, which places similar numbers next to each other
W5
Why? → There is no poka-yoke or zone separation for high-confusion SKU pairs
ROOT CAUSE
The warehouse layout creates adjacency between visually similar, easily confused SKU pairs with no error-proofing.
CORRECTIVE ACTION
Separate all high-confusion SKU pairs by at least 3 bin locations. Add large-format colour-coded labels and a barcode scan confirmation step before pick completion.
EXAMPLE 4
Problem: A weld failed in the field causing a product recall
W1
Why? → The weld did not achieve the required penetration depth
W2
Why? → The welder set the amperage 15% below specification
W3
Why? → The specification is written in a binder in the supervisor's office, not at the workstation
W4
Why? → Standard work sheets are printed annually and stored centrally to avoid "clutter"
W5
Why? → There is no policy requiring standard work to be visible at the point of use
ROOT CAUSE
Standard work documents are not required to be visible at the point of use, so operators work from memory rather than specification.
CORRECTIVE ACTION
Implement a visual management standard requiring all critical parameters to be posted at the workstation in laminated format. Audit compliance monthly.
EXAMPLE 5
Problem: Lead time for a key product jumped from 4 days to 11 days
W1
Why? → A critical sub-assembly is sitting in a WIP queue for 6 days before final assembly
W2
Why? → Final assembly is running at 60% of normal capacity
W3
Why? → Two of four assembly operators are on extended leave simultaneously
W4
Why? → Leave was approved without checking production demand or cross-training coverage
W5
Why? → There is no system to flag when approved leave creates a capacity gap against the production schedule
ROOT CAUSE
The leave approval process does not account for production capacity or cross-training gaps, so capacity shortfalls are only discovered after lead times deteriorate.
CORRECTIVE ACTION
Integrate leave approval with the production scheduling system. Require supervisor sign-off confirming adequate cross-trained coverage before leave is approved during peak demand periods.
EXAMPLE 6
Problem: A new operator produced 200 scrap parts on their first solo shift
W1
Why? → The operator set the press tonnage incorrectly
W2
Why? → The operator was not confident about the correct setting and guessed
W3
Why? → Training was completed but the operator never set the tonnage during training
W4
Why? → The trainer skipped that step because the machine was already set up when training began
W5
Why? → The training checklist has no requirement to verify the operator can perform set-up from scratch, only that they observed the process
ROOT CAUSE
The training checklist measures observation, not demonstrated competence. Operators can be signed off without ever performing the task independently.
CORRECTIVE ACTION
Redesign training sign-off to require demonstrated competence: operator must perform each critical task from scratch, unassisted, while the trainer observes and verifies the result.
The pattern you'll notice
Look back at all 6 examples. Every single root cause points to a system or process failure — not a person's failure. The operator who guessed the tonnage setting wasn't careless; the training system never required them to prove they could do it alone. The picker who selected the wrong SKU wasn't distracted; the warehouse layout made the error almost inevitable.
This is the point of 5 Why. When you reach the real root cause, the corrective action becomes obvious — and it changes the system, not just the person.
If your 5 Why analysis ends with "operator error" or "employee didn't follow procedure," you haven't gone deep enough. Keep asking why.
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