Root Cause Analysis and Corrective/Preventive Action
What the exam tests
The logic of a full corrective action loop: containment, cause identification, occurrence versus escape cause, implementation, and effectiveness verification. Expect case-based questions and tool selection.
Core rules
- Sequence: contain to protect the customer, define the problem with data (what, where, when, how much, and is/is-not), find the occurrence cause and the escape cause, implement, then verify effectiveness over time.
- Tools: 5 Whys for linear chains backed by evidence; fishbone (man, machine, material, method, measurement, environment) for breadth; fault tree analysis for deductive top-down logic; Pareto to focus; FMEA to prevent recurrence by revising severity, occurrence and detection ratings.
- AIAG-VDA FMEA replaces the RPN (S x O x D) with Action Priority (High/Medium/Low) derived from the S-O-D combination, because multiplying ratings has no physical meaning.
- 8D tracks the disciplines from team formation to recognition; A3 summarizes the same logic on one page. Corrective action removes the cause, correction fixes the defect, preventive action addresses causes that have not yet produced a defect.
Worked example
Fasteners on an assembly line are found under-torqued. Why 1: torque below spec. Why 2: the torque wrench was out of calibration. Why 3: the calibration recall schedule was not maintained. Why 4: no named owner for the calibration system. Why 5: the procedure named no responsibility (system cause). The escape cause is separate: there was no end-of-line torque audit. Actions: assign ownership, automate recall, add dynamic torque monitoring with error-proofing, and confirm with 30 days of audit data.
Traps that cost marks
Stopping at "operator error," which names a person rather than a system. Claiming a root cause without evidence. Skipping the escape point, allowing the same defect to reach the customer again. Closing the CAPA without an effectiveness check. Treating run-of-the-mill FMEA RPN thresholds as a standard when the customer requires Action Priority.